Hey they did support it until they were getting difficult legal contacts because some users were abusing it, and getting turned away by different hosting providers.

They shut it down to protect the rest of us who use it without abusing it.

https://mullvad.net/en/blog/removing-the-support-for-forwarded-ports

Unfortunately port forwarding also allows avenues for abuse, which in some cases can result in a far worse experience for the majority of our users. Regrettably individuals have frequently used this feature to host undesirable content and malicious services from ports that are forwarded from our VPN servers. This has led to law enforcement contacting us, our IPs getting blacklisted, and hosting providers cancelling us.

The result is that it affects the majority of our users negatively, because they cannot use our service without having services being blocked.

I know the port forwarding thing can be a deal-breaker for some people, but it's not Mullvad's fault that they needed to remove this to be able to continue providing quality services for the rest of their customer base.

This is sadly one of those "this is why we can't have nice things" type deals because when enough people abuse it, it becomes a problem. I have no ill will towards Mullvad for taking it away when it became financially and legally foolish to continue doing so.

This is to be honest a huge barrier for me.