Badge display mode

Hello,
I have a Problem with K9mail. I am unable to become a badge displayed when new mails come in, wether dots nor numbers, while it works perfect with all other apps.
The settings are all the same.
Thanks for some advice.

Huawei Mate 20 Pro. LYS-L29
EMUI 12.0.0.142 (C432E3R1P2)
Android 10