Why don’t you just use Shelter to create a work profile on your phone? The work profile can have a second vpn connection. I do this with my homeserver. The apps that connect to the home server are installed in the work profile so they have permanent access to the homeseraer while the normal profile is on my external vpn.

If it’s for your personal use and no one else is going to connect, why don’t you just configure a wireguard tunnel to remotely connect to your server as if you were in LAN without exposing anything?