@nprofile1q... Federation works fine with proxying.
With Mastodon you just tunnel Puma and Streaming over wireguard to your frontend VPS while the backend sits on your home network.
Then for the sidekiq queues you use wireguard and tunnel 0.0.0.0/0.
Same principle for other fediverse software like IceshrimpNET.
I have no idea about Synapse though, sorry.