I've been looking at security keys like the Solo V2, but it looks like my email provider Mailbox.org doesn't support (and never will support) anything other than their utterly crappy 2FA with a 4 digit PIN and a random 6 digit sequence[1].

If only there was some other service as good as Fastmail, but with humane prices.

1. https://userforum-en.mailbox.org/topic/lets-talk-about-2fa-on-this-website-again