So I have this setup:
Mikrotik router, model RBD52G-5HacD2HnD - latest firmware
USB LTE Modem Huawei e3372h-153 - unknown firmware

I have prepared the router by inserting the modem to USB and resetting the router to default settings using a user button.
I use router's native web interface to set it up.

The problem I have is:
a) Once it boots, LTE interface is working, so I just configure a bridge between LAN and LTE. Suddenly I get internet on my network. However I need to set a custom APN to get static IP from provider.
I go to Interfaces -> LTE -> Edit, and select the APN. Once I hit [Apply], the view refreshes and my changes disappear. Same happens if I "enable" any of network modes. See screenshot...

Also I am not sure what "functionality: minimum" means and if this is the source of my problems. If so, how do I fix this?

b) I also tried to switch the interface to QUickSet and change the mode from "Home AP" to "LTE AP". Once I apply changes, web interface is no longer available after it reboots.

Should I attempt reflashing the modem? Have not looked in to it yet. It does have a proprietary branding silkscreened on it, by one of providers.

the APN profile is a drop down list that provides choice of preconfigured APN profiles, you should configure a new APN profile first, then select it

This can be done in "interface -> LTE -> LTE APNs -> Add new"

Also, QuickSet in your version did not yet support dual band LTE AP devices, like yours, a newer RouterOS version is required to be able to use the QuickSet

Yes, I have added an APN in APNs list and I can select it in interface settings. However my selection disappears when I apply the configuration.

I have just figured out my modem is working in HiLink mode instead of stick, and it offers web interface of it's own. So I have set the APN there and it seems to work.
Not sure if I should investigate this further to reflash it for Stick mode, the benefits (in comparison to time wasted) are not clear to me yet.