On 20.6.18 MIUI 12 Weekly on Mi 9T.
I have setup Google Discover feed on the page left to home.
Kept getting annoying message "YouTube keeps stopping" with the options to Report to Xiaomi or Cancel.
Clearing Data for YouTube app in Settings did not solve the problem.
Solution: uninstall and...
Watched your video and tried to reproduce the problem on my Mi 9T running 20.6.4. And I can't. Unlocking animations work every single time on my Mi 9T, with fingerprint unlocking.
So it must be something you have configured or installed.
No flickering either way here on my Mi 9T with 20.6.4. That suggests it is something that you have configured or installed that is causing the problem.