I used it too. I miss it, but i get why they removed it: it just kinda breaks the Signal user experience and trust model. This app lives and dies by the users trust their conversations will be private. By having an option to message someone in a completely unencrypted, easy to intercept mode like SMS it risks this trust for little gain (some power users like us liked it). By removing it, the app concentrates on what is expected from it and removes a big possibility for user error while fleshing out its marketing image even more. It makes perfect sense but its a tad annoying.

Get a 10GbE nic and OpenVswitch

Easiest Solution imo:

• get Wildcard DNS, point it to the public IP of your NAS
• deploy the ssl cert (containing your main domain and sudomains for your docker containers)
• configure reverse Proxy in Synology configy proxying requests for the subdomains to your docker container (you can enforce only local access to certain services too)
• Static route or local dns (Pihole) to redirect local requests for your public ip to the private IP of your NAS
• done!