Synology NAS VPN Server package only supports PPTP, OpenVPN, and L2TP/IPSec in the provided knowledge base; there is no Synology NAS WireGuard server setup article here.
What the fragments do say:
- Install VPN Server from Package Center > All Packages > VPN Server.
- Choose OpenVPN or L2TP/IPSec.
- Configure port forwarding on your router to your Synology NAS.
- For OpenVPN, clients need an OpenVPN client; for L2TP/IPSec, Windows 10 has a built-in client.
- Synology also says you can connect your NAS to a VPN server as a client, but not as both server and client at the same time.
For WireGuard specifically, the only related solution in the knowledge base is to use a GL-iNet router on the same LAN as the NAS, set up the GL-iNet as a WireGuard server, and then connect your phone/Windows/etc. as WireGuard clients to reach your home LAN and DSM.
Sources used: [1], [2], [6], [12]