If you mean that you are using Proton VPN on your Raspberry Pi to mask your downloading traffic, then no that same VPN will not help you access services like Jellyfin on your home network while you are remote.

Instead you'll want to use something like Tailscale (or Wireguard). You run it as a service on your home network and it then becomes your own VPN that you (or others) can use to connect to your home network when you are remote.

You could run Wireguard on the same RaspberryPi that you use for downloading but I would recommend against it assuming that you're running Proton VPN right on the host itself (and not inside a container).

Not in the way you’re probably thinking, no. The VPN (like Proton) will be isolating devices from each other. This is by design, so you don’t end up in situations like different customers seeing each other on the network.

Your router might be able to act as a VPN host. This would allow you to connect to your home network from anywhere, and use it just like you would use a service like Proton. And if your home network is set to allow devices to see each other, then you could see your Jellyfin server. See if your router can run Tailscale or can act as a WireGuard (or OpenVPN) host. Tailscale will be the most straightforward approach, but not everything can run it. Worst case scenario, you could just run Tailscale directly on your Jellyfin server.

The big issue with requiring a VPN is that it makes remote access on some devices difficult or damned near impossible. For instance, good luck getting a smart TV to run Tailscale. Tailscale will be fine for things like phones, laptops, or tablets. But if you have a smart TV you want to remote view things on, you may need to consider a reverse proxy instead. And a reverse proxy is such a rabbit hole that it would deserve its own post.