Mi 11 Ultra: no sound anymore

Hello.
Yesterday my Mi 11 Ultra suddenly stopped producing any sounds.
I cannot hear any voice calls, music, ringtones, notifications, youtube sounds, the phone speaker is just totally silent.
The mic keeps working.
The sound works OK through bluetooth headphones.
So there must be something with the speaker.
A reset to factory settings didn't help.
My MIUI is 12.5 | V12.5.12.0 RKACNXM.
Do you think it is a 100% hardware issue? Can it be reparable?
Thank you in advance for your help.