Hello!
I found a way to bypass "sync has accored a problem" try to:
Reinstall OperaGx;
Repeatedly input the password to confirm identity when sync;
Put on custom and check on all checkmarks.
This should work, again you need to repeatedly try to sync, so try as many times as possible to sync into your account, aswell reinstalling operagx will most likely fix it but if not make sure all data/files of operagx are deleted for a full resintall since reinstalling the normal way won't exacly work. If OperaGx doesen't work even all your attempts then i suggest:
Using a different browser like chrome;
Finding a toturial (visual or not) ((I also had a problem so you might need to use cmds of your computer to bypass somethings to get fullaccess to Opera gx)).
But a alternative, it may sound stupid but it does work sometimes. Uninstall and delete all OperaGx files, use a temporary browser and wait for maybe a couple days and reinstall OperaGx and see if it works.
Again im not a Tech Wiz or specialized in this sort of stuff but and hopefully you will get OperaGx Working how it should.
Your most stupid person on earth
-Gbm