The following has worked in the past for this issue:

Goto the URL opera://about, take note of the "install" path, and close Opera.

Hit Windows key + r to open a run dialog, type cmd and press enter.

Then, type the following and press enter to start Opera:

"C:\Program Files\Opera\launcher.exe" --show-component-extension-options

(Adjust path to your launcher.exe based in your install folder that you took note of earlier.)

Then, once Opera starts, wait 30 seconds. Then, goto the URL opera://extensions, turn on developer mode, and click "Update" at the top of the page.

Then, goto the URL opera://about and check for updates. If there's an update, let Opera update. If there's no update, don't worry.

Then, when all done, restart Opera.

@ravenrei https://forums.opera.com/post/298643 should be some general things you can try.

Confirmed in Opera GX and Opera Stable. Works as intended in Opera Beta and Opera Developer though.