Scan your system with the free version of Malwarebytes.
In Opera, goto the URL opera://extensions and remove any extensions that shouldn't be there. Then, restart Opera and make sure the extensions you remove don't come back.
If the extensions come back, goto the URL opera://about, take note of the "install" path, and close Opera. Then, uninstall Opera (do not choose to delete your data when uninstalling) and delete the install folder if it remains. Then, reinstall Opera.
If the problem extensions still come back, goto the URL opera://about, take note of the "profile" path, goto the URL opera://extensions, remove all extensions, close Opera, delete everything in the "Extensions" folder in the profile folder, start Opera, goto the URL opera://settings/reset and reset your settings.
If that doesn't work, while Opera is closed, rename your profile folder so that Opera creates a fresh one.
If none of that works, until you can find the infection on your computer, go into Opera's install folder, right-click launcher.exe, choose to create a shortcut, move that shortcut to your desktop, right-click the shortcut and rename it "Opera GX Safe Mode", right-click the shortcut again, goto "properties", switch to the "Shortcut" tab, and edit the target field's value to be:
"C:\Program Files\Opera GX\launcher.exe" --disable-extensions(Adjust the path to your Opera GX's launcher.exe using the "install" path in opera://about as a base.)
Then, only open Opera with that shortcut until things are fixed.