New Webmail is a hot mess! What did they do intentional sabotage the webmail? I can’t open emails without the dreaded spinning wheel, deleting messages now without the box to check is more cumbersome...
I suggest looking into Gmail as well. I have Proton and the one thing I have noticed about it is if you forget your password, you can't access your old emails. This is good for security but bad for convenience. See here for more info.
You can change your password if you know your old password and then you can access your old emails. However if you DON'T know your old password and have to reset it via the app, then you can't access your old emails because the encryption have changed.
You can use it with a client via POP/IMAP as per here. Seems to even come with a free app that allows end to end encryption. Doesn't look as user friendly as setting up Gmail on a client though. Also, not sure if you can load non-Proton accounts into the webmail UI like you can with Gmail.
Do you still use Thunderbird?
No, not anymore, although I hear there is a new Thunderbird UI out. Might try it just for fun. ::edit:: Downloaded the new Thunderbird and it was a easy setup with Gmail. So far liking the dark theme but still getting used to the new UI.