Ah yeah, this was the line I read a bit too fast:
Any modern Linux distribution should basically be in good shape for the AMD Ryzen 9000 series processors. The one recent caveat is needing Linux 6.12+ for the AMD Zen 5 CPU power reporting if that is important to you otherwise it’s an easy one-liner patch to backport.
SnappyMail seem to be a fork of Rainloop and both Rainloop and Snappymail appear to allow multiple providers - https://snappymail.eu/
Cypht seems to be a similar solution where you selfhost a webserver that acts as a web client to external email providers - https://www.cypht.org/documentation/
I find nothing about push notifications for either of those solutions though, and I’m not sure about how much the webclients cache.