I have the same problem.
Even if I just open 3-4 tabs, the operation is very slow and may crash.
Reinstalling several times did not help.
Reverting to 77.0.4054.277 solved the problem.
Disabling the automatic update schedule is mandatory.

Sorry for the late reply.

I uninstalled the new version and installed the old version.
Old versions are available here.
https://get.opera.com/ftp/pub/opera/desktop/

To stop automatic updates, disable "Opera scheduled Autoupdate".
Control panel > management tool > task scheduler

I have the same problem.
Even if I just open 3-4 tabs, the operation is very slow and may crash.
Reinstalling several times did not help.
Reverting to 77.0.4054.277 solved the problem.
Disabling the automatic update schedule is mandatory.