Thinking about dropping Gmail, but it's killer feature is its excellent search capabilities. Looking at OSS solutions, none seem to have search that even comes close.
I can usually dig up a several year old email in a few seconds, including time to fiddle with the query to get what I'm looking for (so multiple searches completed in, like, 5 seconds.) That's hard to beat .
@teleclimber IMAP is definitely good for choice of client. You might also look at astroid which is gtk and neomutt, which is curses, both notmuch backed
One of the first Mastodon instances, there is no specific topic we're into, just enjoy your time!