@richardmphopheya You can try everything above. For @Clayn's method that worked, that would look like the following on macOS:
Open up Finder, hit command + shift + period to enable the showing of hidden files and folders and browse to "/Users/yourusername/Library/Application Support".
In there will you Opera GX profile folder. Something like "com.operasoftware.OperaGX"
While Opera is fully closed, you can rename that folder to "com.operasoftware.OperaGXOld", start Opera to let it create a new "com.operasoftware.OperaGX" folder. Then, fully close Opera, select everything in "com.operasoftwareOperaGXOld", copy and paste into the new "com.operasoftware.OperaGX" while choosing to overwrite existing files for everything.
There's also this macOS issue that affects cookies. It might also affect Local Storage, but I'm not sure.
For the standalone installation test mentioned in a previous comment, on macOS, you'd open a terminal and run a command like this:
"/Applications/Opera GX.app/Contents/MacOS/Opera GX" --user-data-dir="$HOME/Desktop/Opera GX Test"I think. I'm not on macOS to test though, so you might have to adjust some things.