How to prevent wireguard VPN client to access local network resources?

Hello
I have Brume2 installed after a main Router and receiving internet from it.
Brume2 network is 192.168.8.x. The main router network is 192.168.0.x.
I have wireguard vpn server running on the Brume2.

At a remote location I use a Mango (GL-MT300N-V2) router as a VPN client running at 192.168.12.1
A PC is connected with a lan cable to the Mango router.
The PC is able to access the VPN connection and can browse internet through it, the internet sites see the ip of the vpn server, which is ok.
However the PC can also access the admin panel of the Mango (at 192.168.12.1) and the admin panel of the main router (at the server local network - 192.168.0.1).

I want the PC to be unaware that it is using a VPN connection.

-On the Mango router can I forbid this exact PC to see the Mango admin page at 192.168.12.1?

-Can I prevent the main router page (at 192.168.12.1) to be accessible through the VPN connection (preferably for a certain device)?

Thank you in advance

Please refer to: