I used to torrent a lot, but gave up after my ISP adopted CGNAT and I lost the capability to forward ports locally. Do people adapted bittorrent to IPv6, since then, to circunvent this problem, or are we still stuck with IPv4 in this space?
Though in ideal cases (ones with high active seeders), that isn't going to affect performance that much. Torrent can also use UDP hole punching, but that can sometimes be finnicky behind CGNATs
I'm not sure if it would work for torrenting but I can't think of a reason why it wouldn't.
The thing is Mullvad offers dynamic Port-Forwarding only. They get to decide what port number they can grant for users and users cannot request for a specific port. There are VPNs that have static port-forwarding which is rare. There are less than 5 VPN providers that have static port-forwarding from what I remember and users can decide what port number they want (unless specific port number is taken prior). It would be a pain if someone have a range of applications that already using specific port prior and would have to change them to use the VPN's defined port number depending on how much applications they have to change.
I have yet to see a torrent client that doesn't let you specify the public port it's listening on.