Mail app setup for third-party email account stuck

I have a working email account on a third-party emailprovider. I can log in to the webmail, so the account is working. I'm trying to add it to Apple's standard Mail app, which I use on other computers with the same email provider — so nothing out of the ordinary.

After I add my info, including the smtp server etc, it shows me this screen. The buttons says 'Done', when I click on it, it changes to 'Next'. Click again, nothing happens. Any ideas how to solve this?

I tried deleting the ~/Library/Mail folder but same outcome. I also tried adding the account inside the Mail app and through System settings, same outcome.

This is a new user account on an Intel MacBookPro from 2019, which was running fine for another user just 2 months ago.