You might want to look at tailscale.com - I'm not 100% certain I understand exactly what you want - but it does allow any client to expose services; assuming no

You might want to look at tailscale.com - I'm not 100% certain I understand exactly what you want - but it does allow any client to expose services; assuming non-server wireguard/tailscale-clients don't expose services/have firewall set up -I think it does what you need? ZeroTier should also be an option.