instead of using F-droid, github and other websites for downloading
Erm … K-9 already has Github downloads, incl. but not limited to Beta releases?
maybe it is even better to release the software via the https://k9mail.app/ website.
a routine work for many softwares (through the official website).
this could be better for the update history and software release
about the four download links: apparently some of them do not work or do not work well already
No idea what you mean? I just tried the 4 links and they all worked and went to the respectives sites and download pages for K-9.