I can tell you right now, having a non-private home LAN IP range is going to drive you nuts.
Your only recourse is to use a SSH tunnel.
In the case of the Synology:
- Control Panel - Terminal & SNMP - Enable SSH
- Using Putty or SSH, you will need to a) Login to the NAS as user admin and port forward 8888:127.0.0.1:32400 (Putty will show it as L8888 I believe for ‘Local’)
- If using SSH itself ssh -L 8888:127.0.0.1:32400 -l admin ip.addr.of.syno
- sign in and let the shell session sit idle, we only need the tunnel.
- Now, in an in-cognito window, open http://127.0.0.1:8888/web
- This will bring you to the Got It and Sign In windows.
- Proceed through until you arrive at the dashboard.
Should you ever need to connect with PMS again and re-claim/re-authenticate, you will need do this.
If you can make the home LAN a proper RFC-1918 LAN, you are much better served. I had always thought RFC-1918 LAN addressing was common in your part of the world.