@leocg No. I don't intend to do those things. That's a bit too much work for what seems like a simple problem and may possibly cause other issues with my computer.

It may seem like a "simple problem", but if it's blocking your use of the browser, it's really not. A basic question is whether there's an incompatibility between Opera and Windows 11 on your specific computer. The Windows 11 upgrade process changes a LOT of things on a system and is known to have compatibility issues with a number of 'driver' software modules that necessarily interface various hardware/software elements with each other and which may be somewhat unique to a given computer installation. If one browser uses one of the incompatible drivers for some reason or in some way but another one doesn't, the two browsers will behave differently. @burnout426 has suggested doing a standalone installation of Opera to find out if there's an inherent incompatibilty between Opera and Win11 on your unique system. If not, the problem cause lies elsewhere.

Moreover, in an OS upgrade, it's possible for some files to become corrupted or be deleted. Since Opera creates and preserves certain of its 'profile' files even across an Opera uninstall/reinstall cycle, corruption within those profile files/folders may persist even after a typical browser reinstall... hence his suggestion to try with a new profile (which creates all-new, default-level files within). Likewise, since browser extensions (whether internal or custom-installed) are software programs in their own right, it's possible they may have their own incompatibility issues in a given installation that's been OS-upgraded. A fresh 'standalone' install eliminates any custom extensions from the issue (while leaving your current Opera installation with its customizations/personalizations intact), and you can readily turn off its internal adblocker to eliminate that possible compatibility issue as well.

The object is to systematically identify and eliminate possible factors that might be causing your Opera problem. Since other users have successfully upgraded to Win11 with Opera, the implication is that there's something unique to your system or Opera profile that's triggering your problem. Though the problem seems 'simple', there's a necessary amount of effort needed to isolate and fix the true cause... otherwise, one is left to merely guess at causes.

Do a test. Make a standalone installation of Opera to a folder named "Opera Test" on your desktop. This will not interfere with your normal Opera. If everything works fine in this test Opera, your Opera profile is most likely corrupted or one of the extensions you have installed is causing the problem.

Also, it wouldn't hurt to uninstall Opera (don't choose to delete your data when uninstalling), and reinstall Opera to fix Opera's program files.