Cannot set up bridge mode with Huawei B818-263 (4G router)

Yes, there are specific situations which having two routers (a "Double NAT") can be a serious problem, such as

• Setting up OpenVPN to log onto the local network from the internet.
• Forwarding ports to share servers on the internet
• Playing certain internet games

Search for "Double NAT" for more specifics.  Users who do not need those specific activities are (literally) unaware that a Double NAT exists and notice nothing.

There are several methods for eliminating a Double NAT, including:

• Putting the Orbi system into Access Point (AP) mode, where the ISP modem/router assigns IP addresses to all devices in the network.  This has the side-effect of disabling all "router functions" of the Orbi,, such as Armor, Parental Controls, Port Forwarding, OpenVPN, etc.  If those functions exist on the ISP device, then "who cares".
• Putting the ISP device into "bridge mode" and having the Orbi be the only router.
• Creating a DMZ on the ISP device that points to the Orbi's IP address.

In all of those cases, most people would opt to disable the WiFi on the ISP device in order to reduce interference.