I still use Thunderbird for my personal email because honestly it’s the best email client I’ve used, and I tried all the popular ones (including Outlook, eM Client, Mailbird, Postbox, Windows 10 Mail, and others). In particular, I have filter rules (Sieve) that filter emails into folders, and many of the clients don’t handle folders well.
On Android, I haven’t found any email clients anywhere near as good as FairEmail. It’s free and open-source, and has every feature you’d need. It directly connects to your provider’s IMAP server so messages don’t have to be relayed via a third-party or Google’s servers.