Thank you both for your answers
I am using 4g remotely so I guess there is no conflict with 192.168.1.x.
I am also using another VPN server in a NAS which is connected to the Asus. In this case, I can reach both the modem and the Asus in 192.168.1.1 and 192.168.10.1 respectively. So it seems...
I use the internet provider's modem/router only as a modem. I have connected the Asus Merlin router AC2900 (WAN port) to the LAN port of the modem. pppoe passthrough is activated in the modem, so the Asus router makes a second connection (pppoe). Everything works great and when I connect to...