Yes, from my PC on site A, I can ping the GL-MT300N-V2 on site B and I can also access the Control Panel of the GL-MT300N-V2 on site B by typing his LAN IP (192.168.10.1) in the address bar .
Therefore the connection should work.

The problem is that I cannot reach webserver2 (192.168.10.25) which is connected to the LAN port of the GL-MT300N-V2 on site B.

So I can’t reach clients on the LAN side of the GL-MT300N-V2 on Site B. But I can reach devices which are connected with the WAN side of the GL-MT300N-V2 on Site B, e.g. the webserver1 on Site B with the IP 192.168.1.25 is reachable from my PC on Site A.

Here is an overview of how the devices are connected.