For torrenting, port forwarding is only marginally important - for torrents which have very few peers and you can connect to none of them.
It's also risky because mullvad certainly has records of forwarded ports and can out you if they receive a properly worded subpoena. There is also a chance those records would be present in their backups even after you deleted the forwarded ports.
I have a separate command for port forwarded torrent client and only use it when absolutely necessary, which is almost never.
How is that relevant here? mullvad has to keep track of who to forward the port to, any NAT ports are going to be ephemeral and conducted through an encrypted tunnel.
It's also risky because mullvad certainly has records of forwarded ports and can out you if they receive a properly worded subpoena. There is also a chance those records would be present in their backups even after you deleted the forwarded ports.
I have a separate command for port forwarded torrent client and only use it when absolutely necessary, which is almost never.