nmap scan of the router's wireguard client IP address - scan executed from the wireguard server where the router's wireguard client was connected to:

# nmap -Av 192.168.100.100
...
Scanning 192.168.100.100 [1000 ports]
Discovered open port 80/tcp on 192.168.100.100
Discovered open port 53/tcp on 192.168.100.100
Discovered open port 443/tcp on 192.168.100.100
...
Not shown: 997 closed tcp ports (reset)
PORT    STATE SERVICE        VERSION
53/tcp  open  domain         dnsmasq 2.83
| dns-nsid:
|_  bind.version: dnsmasq-2.83
80/tcp  open  http           BusyBox http 1.19.4
|_http-title: Did not follow redirect to ...
| http-methods:
|_  Supported Methods: GET HEAD POST
443/tcp open  ssl/tcpwrapped

nmap scan of the router's LAN client 'NAT Enabled = YES' in router's wireguard client config - scan executed from the wireguard server where the router's wireguard client was connected to:
# nmap -Av 192.168.0.220
...
Scanning 192.168.0.220 [1000 ports]
Discovered open port 22/tcp on 192.168.0.220
Discovered open port 111/tcp on 192.168.0.220
...
Not shown: 998 closed tcp ports (reset)
PORT    STATE SERVICE VERSION
22/tcp  open  ssh     OpenSSH 8.7 (protocol 2.0)
| ssh-hostkey:
...
111/tcp open  rpcbind 2-4 (RPC #100000)