@namichel Care to share the link that doesn't work so we can try it?

@martant Are you running the VPN while trying to update?

These are my specs. I was able to get it to install. The reason you are not able to install is because Mavericks supported 32-bit. https://support.apple.com/en-us/HT208436#:~:text=Apple has been working with,no longer compatible with macOS.
The new Opera Software is most definitely 64-bit. As you are showing me here "Betriebssystem: Mac OS X 10.9.5 64-bit"

Also the fact you are getting an "error occurred proofing updates" that means there is something wrong with your Opera Application. Have you tried uninstalling it? Have you tried installing earlier versions of Opera instead of V 49.0? Like I said I was on 30 so try that. You should have no issue with it updating automatically since you can't even get it to do that manually.

@martant I'm thinking don't update yet. Try to get Opera fixed before you update your OS and get stuck with it.

What I would try is to click Opera in the top bar while it's open.
I click Opera>About Opera
It then takes you to where it tells you which version you are running. On my iMac it was Version 30 something. All I did was click on Relaunch and it updated to like version 45. This still wans't the latest version when I went back to Opera>About Opera so it asked me to relaunch again Then it updated me to version 55. After the relaunch I opened About Opera again and it said relaunch again so I did and then I was on version 75. What you can do if this works for you is stop when you get to the versions 50+ if you are saying that is all that will work on Mavericks.

Like I said my iMac is on El Capitan and version 75 still works fine. I read in the Opera Support Documentation that it is recomended that all users update to the latest version of Opera so I wasn't aware of certain versions being only available for certain Operating Systems. I was looking for the documentation on which version is for Mavericks to help you out; I searched all night and couldn't find this information.

@leocg
I'm wondering if it Opera would update on it's own to the version supported by the OS no?
I was on Version 34 on my iMac late 2012 currently running El Capitan and it updated to version 51 without issue. It's now on version 75 and I'm currently using it to type this message. I just had to keep going back to About Opera and clicking that Relaunch Now button until it was up to date.

@puresk You might get help if you used a spellcheck or attempted to make sense when you type.

To try and help you here, what is this setting set to?

*Edit: I just enabled this setting because I have no use for it and it worked for me. So I would say go to
Settings>Privacy and Security>Cookies and other site data
and make sure that Clear cookies and site data when you quit Opera option is not on.

@leocg Understood.

@leocg It's actually funny that Vivaldi which relies on Chromium can have this developer menu

@leocg Chromium is open source. Is it not?

@leocg ok, I understand how to enable and disable extensions. The problem is it is an extra step. I think the icon in the taskbar should allow you to do this to eliminate that extra step required if it is going to take up space on the taskbar. There are a ton of icons up there already.

So I feel the extension button is useless if it doesn't do anything besides showing and hiding extensions from the taskbar. If there is a way to hide the extension button then please let me know.

To further explain since my point is not getting across, this menu here could benefit from a simple on and off switch for extensions instead of just an unpin button. The only thing that I wish to unpin would be the Extensions Button that has no benefit to me. I don't need to hide the Extensions that I use and I only use 2.

Suggestion

I love how Safari's Developer Mode breaks down the resources and elements for you. They even categorize them. Is there anyway we can incorporate this into Opera's Developer Mode?

Example of the Mac version:

It breaks it all down for you so you don't have to guess what is what reading that huge HTML code that Opera gives you when you click Developer>View Source

It's just Apple has ruined Safari and made it unusable so I prefer to use Opera on my Mac for a smoother experience.