This ends with fairly good news, so please excuse the length.
I have run Developer and Stable in Kubuntu and other distributions for years. I have always installed via the deb files. from the Opera website. Every now and then, Developer became difficult to use because of an issue so I reported it and used Stable until it was fixed.
A recent Developer update removed the Home Page icon and this was reported via the Developer bug pages. Then I noticed that Developer menus and other text items were much smaller than the system fonts: also reported.
The fonts issue was resolved. A couple of updates later, pages were not rendering properly. In particular, some jpeg images were not rendered. I could not use the bug reporter as this was one of the affected sites. Neither could I view news sites and weather report sites. More significantly, I could not manage my bank account nor make on-line purchases (esp. where Captcha was used).
I decided to move everything to Stable until the issues were resolved. Stable was even more unusable.
I have been using Firefox while I waited for a resolution. I have not seen anyone else publish similar problem.
I finally gave up waiting and decided to reinstall. Developer only allows the export of Bookmarks and so I knew I would lose all my passwords and settings.
I used the Muon Package Manage to reinstall both packages to no avail. No mixture of uninstalling reinstalling or purging solved the problem. I could not even use the startup setting pages. Eventually, Developer crashed every time on opening. without giving time to add notes to the crash report.
My fix was to purge/uninstall everything in muon and use the Snap version that has appeared. in their repository. The issues are that there is no way to install both Stable and Edge. Also, the Home Page icon is missing with no way of adding it in Settings or other menus. Page rendering and menu fonts are fine. I have stuck with Stable as I don't want the chance of losing my preferred browser.
Also, although the 'Instructions on posting about problems in Opera for Linux' advice at the head of this sub-forum says to save bookmarks, passwords and settings, there is no way of doing that with Opera Stable: the same issue I had with Developer. Also, it suggests resetting the settings to default. Again, there seems to be no way of doing this in either version.
I am wondering if the Developer and Stable deb files are no longer supported in favour of the Snap versions. It would also be helpful if the saving of bookmarks, passwords and settings was possible.
This has come to you via a fully functional Opera Stable.