How could I debug this when both my ISPs don't support IPv6?
I don't think it crashes because of IPv6 but another problem, I can't check because I can't even connect though 😕

Ok, I got helped, it worked with a VPN.

As expected it had nothing to do with IPv6, the server is just missing vapid keys. So here is a PSA for all Mastodon admins: Make sure your server has vapid keys set, or Tusky 19.0+ (and likely all other apps that use push notifications) will not work with it. How to generate those keys is explained in the Mastodon documentation:

@ConnyDuck I can't tell if vapid keys are an actual thing or if you're just making fun of them.

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