I've updated my Mi10 to weekly 21.1.6 and push notification stopped working.
I've enabled all permissions, disable all battery optimizations, but push notification doesn't appear.
When I open the app (such as WhatsApp or telegram) it instantly update and push notifications appear.
It was difficult: I went by trial and error.
After some fails, I used TWRP-3.4.2B-0623-XIAOMI10-CN-wzsx150.
Before booting from TWRP (don't flash it!), remember to disable password, PIN and fingerprint: this way, TWRP is able to decrypt data partition.