Unless you never want to torrent, I would say to not use mullvad, you can't forward a port with them (same with NordVPN). There are plenty of VPNs that don't log and allow port forwarding. I use AirVPN.
I’ve not encountered any issues filling up my NAS with torrented Linux ISOs via NordVPN?
My priority for a VPN has just been no logging and the ability to ‘travel’ internationally.. so if there the case, no need to rush out and switch then?
A connection has to be established. That is only possible if one side has an open port.
So you can basically not connect to other people with closed ports, which reduces your available pool of people to connect to.
As long as there are enough people with open ports for you, you and the torrent ecosystem will be fine. But when nobody or very few people have open ports, torrenting simply doesn't work.
They've done other things, but the reason I don't use Nord is that they had a breach where an attacker had physical access to one of their servers, and they tried to sweep it under the rug rather than notify users.