How to set up a bunch of Microt (router) + Microt ("modem") + LTE?

Question

Computer networks

Help with advice, please. There is:

• Mikrotik hEX S - I want it to be a router (DHCP server)
  
• MikroTik hAP ac lite (with an LTE modem connected) - now it is a router, but I want it to be just a wi-fi point and a box where an LTE USB modem is plugged in (that is, not the main router, at least).
  

Is this possible and what needs to be configured for this, where to dig?

Answer 1

You want something weird, you want one device to be both an LTE link bridge and an access point, but another device must do the routing. You can do it, but why? Isn't it easier to make Mikrotik hEX S a regular switch?

Answer 2

If you really want a router with LTE support to become a stupid box with a modem plugged in, then disable DHCP on it, assign a static address to it, and on Mikrotik hEX S, respectively, enable DHCP and Internet distribution (setting in normal router mode).
But what's the point in that? And if you need a backup - LTE in the event of a failure of the main Internet channel?
In this case, you will have to create some kind of rule or script that, in the event of an Internet drop, distributes a new gateway address to all clients - this will be the address of the very box with the modem plugged in. Moreover, as far as I understand, until the clients distort the connection, their gateway will remain the old one, and everyone will sit without the Internet until the cable is plugged into the network card. Wi-Fi, respectively, will also need to be reconnected.
But you don't have to arrange this whole zoo if you leave everything as it is - an LTE router can switch from WAN to LTE itself when one interface fails.
It's not entirely clear what you want to achieve with this - like there is some kind of function in one device that is not in the other, so do you want to do castling?
I have never been on “you” with Mikrotiks, and maybe there such buns are made once or twice, of course, then I will turn out to be wrong, but it’s even suspicious.