System specs for testing:

• 'Classic' Mac Pro 2012 tower {Intel Xeon 6-core CPU; 48 GB RAM}
• macOS High Sierra 10.13.6 (Build 17G14042)
• Opera for Mac 75.0.3969.93 or later, but prior to the latest (so that an update would be available)

Description of the (possible) issue:
[This Auto-Update issue is seemingly different from the recent 'damaged application' problem that had been reported for macOS Catalina & Big Sur prior to their latest patches.]

At some point during my use of Opera for Mac 75.x (can't recall the detailed version/build number, but it was likely prior to 75.0.3969.x), I received the usual macOS notification from Opera that an update was available and to relaunch now. Upon clicking that notification's relaunch button, Opera eventually started up again as usual.

However, IIRC, it then automatically displayed (or perhaps I'd manually invoked) either the About page or the Update & Recovery page, showing that the version hadn't actually changed and that the update was strangely still available. Clicking the U&R page's 'Check for update' button merely soon reverted to the page's original state, and further attempts just kept doing the same, without ever actually downloading or initiating any update.

After that failure, I'd manually downloaded & installed Opera Mac 76.0.4017.175, and just continued on my merry way. Today, I happened to invoke the U&R page, where it said that an update (to 77.0.4054.64) was available. Unfortunately, clicking the 'Check for update' button just led to the same behaviour as before, where nothing was actually downloaded or initiated.

There were never any error messages displayed. However, I just belatedly took a look in my Opera profile folder, and noticed an 'opera_autoupdate.log' file which contains the following three messages {although I'm not sure whether they're relevant / significant, or might have occurred with successful updates too}:

[91116:775:0611/125030.740275:511668260192710:ERROR:icu_util.cc(179)] icudtl.dat not found in bundle
[91116:775:0611/125030.741356:511668261078040:ERROR:icu_util.cc(243)] Invalid file descriptor to ICU data received.
[91116:775:0611/125031.546633:511669066339212:INFO:protocol_impl.cc(780)] Main update resource available: false
Steps To (Try To) Reproduce:
This issue is probably not model-specific, and so might be reproducible by using any Mac running the above macOS and Opera versions.

Other Notes
I also did some brief further testing with a couple of older Opera Mac versions available in the Opera Download Archive. I "saved" my profile & Cache folders by temporarily renaming them. After each test, I deleted the re-created profile & Cache folders, starting afresh each time. I can confirm that, at least on my system, Opera Mac 74.0.3911.232 does auto-update successfully (to 77.0.4054.64, currently the latest version). By contrast, on my system, Opera Mac 75.0.3969.93 cannot do so, instead exhibiting the symptoms described above. So, for me, apparently this issue arose some time between those two versions. I'm sorry I don't have any earlier 75.x versions to test with and narrow this down some more.

I'm also wondering whether the time-frame of this issue has anything at all to do with perhaps when some build of Opera 75.x first introduced support for Apple Silicon / ARM (M1) support via any Universal 2 binar(y/ies)?

I'm using Opera Mac 89.0.4447.38 (x86_64) under macOS 11.6.7 (Big Sur) on a MacBook Pro (Mid 2015) 15" laptop. I've also tested with both my normal profile {having two extensions always disabled (built-in 'Opera Crypto Wallet' & third-party 'Mask as Chrome'), and the third one temporarily disabled (built-in 'Opera Ad Blocker')} as well as a brand new profile {where all settings are default and all extensions are also by default disabled / non-installed}.

Opera Mac has a relatively minor issue with the Netflix web player's pop-up episodes-list, when playing a TV series episode. {It's available via a button at lower right (between the 'Next Ep.' & 'Audio / Subs' ones) and lets us see our position within the season or even switch away to playing another season / episode.}

When it's shown, Opera Mac doesn't display episodic progress {i.e., red portions} within the mini progress-bars at the right of every episode {although luckily Opera does do so in the series page's episodes-list(s)}.

Note that Firefox Mac 102.0.1 correctly displays such in-player episodic progress; indeed, I recall that older Opera 77.0.4054.64 {& possibly some subsequent versions} at least under macOS 10.13 (High Sierra) on my dearly-departed 'classic' Mac Pro (Mid 2012) desktop tower also used to do so, and I'd really appreciate it if this regression could be addressed.

Other Notes (Follow-up):

Okay, a bit more testing has revealed something rather interesting that explains why most people probably wouldn't experience something similar.

It seems that at least Opera Mac 75.0.3969.93 & later versions prefer to be on the current startup volume, for Auto-Update to work. From my limited tests, Opera doesn't have to be in '/Applications' though; it can be located elsewhere on the startup volume.

I've been keeping Opera located on a secondary non-boot internal volume, and thus ran into this issue. Also, again in my limited tests, launching Opera 75 from any of my external volumes led to Auto-Update failure too.

So, there's a fairly straightforward workaround, which is to store Opera on my main boot volume. Although, this change in its expectations might be an unintended regression, perhaps from Opera Mac 74.0.3911.232.

System specs for testing:

• 'Classic' Mac Pro 2012 tower {Intel Xeon 6-core CPU; 48 GB RAM}
• macOS High Sierra 10.13.6 (Build 17G14042)
• Opera for Mac 75.0.3969.93 or later, but prior to the latest (so that an update would be available)

Description of the (possible) issue:
[This Auto-Update issue is seemingly different from the recent 'damaged application' problem that had been reported for macOS Catalina & Big Sur prior to their latest patches.]

At some point during my use of Opera for Mac 75.x (can't recall the detailed version/build number, but it was likely prior to 75.0.3969.x), I received the usual macOS notification from Opera that an update was available and to relaunch now. Upon clicking that notification's relaunch button, Opera eventually started up again as usual.

However, IIRC, it then automatically displayed (or perhaps I'd manually invoked) either the About page or the Update & Recovery page, showing that the version hadn't actually changed and that the update was strangely still available. Clicking the U&R page's 'Check for update' button merely soon reverted to the page's original state, and further attempts just kept doing the same, without ever actually downloading or initiating any update.

After that failure, I'd manually downloaded & installed Opera Mac 76.0.4017.175, and just continued on my merry way. Today, I happened to invoke the U&R page, where it said that an update (to 77.0.4054.64) was available. Unfortunately, clicking the 'Check for update' button just led to the same behaviour as before, where nothing was actually downloaded or initiated.

There were never any error messages displayed. However, I just belatedly took a look in my Opera profile folder, and noticed an 'opera_autoupdate.log' file which contains the following three messages {although I'm not sure whether they're relevant / significant, or might have occurred with successful updates too}:

[91116:775:0611/125030.740275:511668260192710:ERROR:icu_util.cc(179)] icudtl.dat not found in bundle
[91116:775:0611/125030.741356:511668261078040:ERROR:icu_util.cc(243)] Invalid file descriptor to ICU data received.
[91116:775:0611/125031.546633:511669066339212:INFO:protocol_impl.cc(780)] Main update resource available: false
Steps To (Try To) Reproduce:
This issue is probably not model-specific, and so might be reproducible by using any Mac running the above macOS and Opera versions.

Other Notes
I also did some brief further testing with a couple of older Opera Mac versions available in the Opera Download Archive. I "saved" my profile & Cache folders by temporarily renaming them. After each test, I deleted the re-created profile & Cache folders, starting afresh each time. I can confirm that, at least on my system, Opera Mac 74.0.3911.232 does auto-update successfully (to 77.0.4054.64, currently the latest version). By contrast, on my system, Opera Mac 75.0.3969.93 cannot do so, instead exhibiting the symptoms described above. So, for me, apparently this issue arose some time between those two versions. I'm sorry I don't have any earlier 75.x versions to test with and narrow this down some more.

I'm also wondering whether the time-frame of this issue has anything at all to do with perhaps when some build of Opera 75.x first introduced support for Apple Silicon / ARM (M1) support via any Universal 2 binar(y/ies)?