Is there any way to seed without access to the router in my building, using Surfshark? Testing using the default port and a couple randomly selected ports, it looks like there is no upnp port forwarding enabled here, and certainly not to my pc. I used to be decently accomplished in IT but I've forgotten most of what I knew.

you can seed over a VPN but most do not allow you to forward a port.
that is not usually a big deal. others that have a port forwarded can connect to you.