Happy Thunderbird user here, and do occasionally send my donations to help keeping my favourite mail client alive.
This is what I do. I use a mail client and forgo web interfaces unless forced. Fastmail is a fine mail provider (I'm cheap and I'm not giving up my 4 grandfathered GSuite custom domain accounts, especially since 3 of them have support for 50 "users" b/c moving the same setup to Fastmail would cost hundreds of dollars a year), but even with them, I would still much rather use a mail client.