So, the problem has been solved, *partially*.
I noticed an interesting thing: even though both browsers consume the same amount of CPU, Chromium UI works and feels significantly faster than Brave.
What I did:
1) revoked all permissions in Nos2x (I use it to log in)
2) Logged back into Brave and now I can see recent notifications and the UI works quickly
In other words, I solved the problem of the freezing UI this way.
But what about CPU consumption? Is this normal? I just opened Profile, without scrolling or doing anything else.
https://video.nostr.build/2269e2abf99e743feb8808fc2092a6d4d345db2318bcacee81592377ecaad2f5.mp4