No signaling for new emails

I am a beta tester.
When new emails arrive they are not signaled. I have no indication about new emails.
When I open K-9 and swipe down, the new emails are loaded.
Is there an explanation and a solution?

I have an internet connection at home that has short “hickups” and k9 seems to loose the IMAP connection sometimes without noticing this (or without finding a way to repair it). Maybe this is something like what I experience.

do you use pull or push for your mail account in K9? Try Push in case you don’t do it already.
Also, it could be that you are suffering issues with battery optimization some Android vendors apply. In that case you would need to exclude K9 from it. Also see:

Thank you stphn.
The hint was the solution. I enabled push, now it worked.
Many greetings