But you don't have to design the backend this way. Especially if you know that you will have to share the binaries when the support for the game ends.
> This effectively bans any third party non redistributable libraries (of which there are many), using many open source licensed projects for the backend
Some games that have been open sourced by the developers solved this issue by replacing such library calls with stubs. I think this is an acceptable compromise.
>What if I rely on steam, or epic for P2P and they shutter the service?
If you still support the game, you can replace those services to keep the game running. If you don't support it (or decided that you don't want to keep supporting it because of the service shutdown), then you just release it with those service calls, and the community will replace them (if they want to of course).