Finally someone figured it out. i stopped using opera Long Ago because of this...incredible no one at opera reads these forums and answers these or has this info in the help file.

so better yet go into privacy and security and under automatic downloads and add Gmail .Com

why on EARTH opera would have this by default is infuriating.....you want peeps to use your browser....why annoy hundreds of millions of gmail users by not letting them download attachments.

I found the setting in Opera and it seems to fix the problem.
Settings > Advanced > Privacy and Security > Site Settings > Automatic Downloads.
I found that there was a block for Gmail. I turned on "Ask when a site tries to download ...." and the block disappeared.

It now works.! Thanks, @tomcha!

If ya use (Yahoo/Outlook/Hotmail/Gmail) as ur primary email.. here ’s how to set it as the default email service in Windows..

If you’ve tried to use links that share content via email (mailto links) you’ve probably run into errors or Windows attempt 'n to open an installed email program..

ya can change default programs for many file types and protocols in Windows..

but (Yahoo/Outlook/Hotmail/Gmail) is not available as an option..

because (Yahoo/Outlook/Hotmail/Gmail) is an email service on the internet..

Note - Since it isn’t installed in Windows.. it’s not an option in default programs..

With a few steps (Yahoo/Outlook/Hotmail/Gmail) can be used as the default email in Windows..

Note - There are two parts to this process - (neither is too difficult)..

1 (1st part) - is to set (Yahoo/Outlook/Hotmail/Gmail) as the default email in your browser..
If you use more than one browser.. set it as the default email in each browser..

2 (2nd part) - is setting your browser (or the one you use most if you use more than one) as the default email in Windows..

(Part 1) - Sets (Gmail) as the default email in your browser (Opera)

1 - Launch Opera..
2 - select the O Menu in the upper left corner of the window..Choose Settings (Alt + P) > Advance > Privacy and security..
3 - In the Privacy and Security section.. open (Site Settings) by clicking on the arrow to the right..
4 - scroll to Handlers and select it..
5 - Toggle the “Allow sites to ask to become default handlers for protocols (recommended)” to On..
6 - Sign in to your Gmail account..

Note - here is what lottsa peeps Miss that Needs to be Done also !..

7 - click the handler icon in the address bar.. i think It's on the right side.. by the star..
It looks like two overlapped diamonds..
8 - when ya hover over it with the mouse.. the pop up says “This page wants to install a service handler”.

9 - A pop up box will appear that says “Allow mail.google.com to open all email links?” choose Allow.

(Part 2) - Sets the default email program in Windows)..

Windows 10
Settings > Apps > Default Apps > Email > Choose the browser you want to use for Gmail.

Windows 7/8
select Start > Control Panel > Programs > Default Programs > Associate a file type or protocol with a program > choose MAILTO under Protocols. Select the browser you want to use for Gmail.

Note - default programs is often listed in the Start menu on the right side..
shorter than go 'n thru Control Panel..

One of these days I may get bold and try deleting my profile on Opera and see if that works

Well, you can test in a standalone installation of Opera without interfering with your normal Opera to know if that will help or not.

Download the Opera installer, launch it, click "options", set "install path" to a folder named "Opera Test" on your desktop, set "install for" to "standalone installation", uncheck "import data from default browser", and install. Test in that Opera, but do not enable Opera Sync, do not install any extensions, do not turn on VPN, do not enable the adblocker and do not import anything.

Do things work fine in that Opera at least?

If so, then something is messed up with your normal Opera profile. You might have to goto the URL opera://settings/siteData type yahoo.com in the quick find field and choose "remove all shown".

You might have to goto opera://settings/clearBrowserData, set the time range to "all time" and clear just "cached images and files". If that doesn't work, you might have to do that for history too. If that doesn't work, you might have to do that for "download history" on the advanced tab. If that doesn't work, you might have to do "site settings" on the advanced tab.

If none of those don't work, you can goto the URL opera://about and take note of the profile path and the cache path. Then, in Windows Explorer, delete the "cache" folder. If that doesn't work, while Opera is closed, in the profile folder, delete "History", "History Provider Cache", and "History-journal". If that doesn't work, delete "Cookies" and "Cookies-journal".

If that doesn't work and you've already tried disabling your extensions, try uninstalling all of your extensions. It's rare, but sometimes an extension can interfere with things even if it's disabled.

If none of that works, you should goto the URL opera://settings/reset and reset Opera to fix its "Preferences" file. You'll lose your extensions this way, but if it's something wrong with the "Preferences" folder in the profile folder, that will probably fix it.

Another thing you can do is open both the "Preferences" in both the standalone installation that work and in your normal Opera with JSONEdit and compare some of the settings like "download" stuff to see if something's out of odd/different. You can then fix it to match and save.

If things don't work in a standalone installation either, try Opera Beta and Opera Developer (click "options" in the installers and adjust things as you want. They get installed separately and won't interfere with your normal Opera) from https://www.opera.com/download to test if it's a bug that's already been fixed.

If nothing helps, it's likely something outside Opera like Sandboxie or Bitdefender or some other security software (even if things work fine in Chrome).

You can also test in Vivaldi to see how things work there. Opera and Vivaldi are a lot alike when it comes to issues they have that Chrome doesn't. If Vivaldi has the issue too, it could indeed be something outside Opera or something with 3rd-party Chromium-browsers.