About the MX Master 3 and the lateral scrolling wheel (aka zoom horizontally). It is not recognized currently, MSFS seemingly does not know about horizontal scroll axis on mice.
However, you can go into Logi Options and create a profile for FlightSimulator.exe and select forward/back. This way, the horizontal scroll whell becomes mouse button 4 and 5. Those you can assign to zoom in / out. But it’s really choppy and not usable at all.
Also, you already have physical button 4 and 5 right below the horizontal scroll whell on the MX Master. I tried mapping those to zoom and unbind the mouse wheel from zooming. That frees the mouse wheel to fiddle with instruments but the two buttons react far too strongly. Long story short, I’ll file a bug to request Asobo to add support for additional axis on mice and stick to the defaults until that happens.