I can't recall when it actually stopped working (maybe around 3 months ago?), but here is the announcement: https://mullvad.net/en/blog/removing-the-support-for-forwarded-ports

Fairly soon after they removed PF, I searched for a show that was less than a year from release, rated over 80% on TMDB & over 8.0 on IMDB, and pretty popular. I couldn't complete a full season of it on any one format (720p, 1080p, x264, x265). Probably around 10 incomplete versions in qBit. Never ran into something that bad before, on a somewhat recent show. Started using usenet and had my files within an hour or so, in the format I wanted. I understand and support their decision, but it was a very good feature to have. If your looking for new material, PF won't affect you. I've read people suggest Tailscale as a way to supplement Mullvad (if you're running a server and want to remotely access it), but I know little about it.