By "completely", you mean that you deleted both the local and roaming "Opera stable" profile folders?
No, just uninstalling including registry leftovers removal. I could try that.
Does your Opera pinned taskbar button point to "C:\Program Files\Opera\launcher.exe" like it's supposed to? You could unpin it, right-click on launcher.exe and choose "pin to taskbar" just to see if it helps.
I did also try to launch the launcher.exe within the path so I assume it's not related to pinning on taskbar. It just won't run the .exe at all for some reason.
What does CrystalDiskInfo say about the health of your hard drive?
Looking at that Chromium bug, do you have chrome://flags/#enable-simple-cache-backend at default or did you change it?
It's set to Enabled now as they suggested on the Chromium platform.