Which?
[Solved]Opera Failing to Minimize | Opera forums
Check the video: Upload files for free - simplescreenrecorder-2021-12-09_04.24.04.mkv - ufile.io (The PC has only Intel iGPU and video-linux driver for it)
It was reported to Opera devs under the BS-23977 Can't minimize Opera window. Fast flickering effect.
No sure that it is Opera bug, but no any other app or browser has it for me.
410082 – Artifacts when settings scale effect on closing
and
445118 – strange flicker in the titlebar under special conditions
are possibly related.