Can the Ethernet leds on the back be turned off?
No.
Hi, asked the same issue for my switch, also mounted at the wall to condert fiber into wire. The only idea was to use a black pen or a piece of tape to cover it. To unsolder it is no good idea and SwOS do not provide anything to dimm it.
AX3 doesn’t run SWOS.
Other then that, those ethernet ports have the LEDs embedded, no way to switch them off except with some masking like paper, tape or stickers (they do exist for that purpose).
Sure, it runs the much more advanced RouterOS, that anyway offers no way to dim those leds.
In this post are you referring to the hap ax3?