OK so that is a private IP its not accessible on the internet directly - which makes sense since you have an ISP router on WAN1 and a BR1 5G on WAN2. This is called double NAT.
Hopefully the WAN1 has a public IP on the ISP router and what you’ll need to do is setup port forwarding on the ISP router from the public IP to the private IP of the WAN1 on the MBX, then you’ll be able to access the web ui.
The 5G connection likely doesn’t have a public IP that you can connect to.
If it was me, I’d pay $5/month to host a Fusionhub in the cloud and then I would setup a client VPN account on the FusionHub so I can access the webui on the LAN of the MBX from anywhere (so long as it has an internet connection).