Can be done, but not with the current firmware and MIDI2LR.
LED can be either on (=127) or off (=0).
Buttons in momentary mode send 127 on push and LED is switched on in the X-touch Mini firmware,
on release the controller sends 0 and LED is switched off.
Buttons in toggle mode sends either 0 or 127 depending on the current state of the LED.
MIDI2LR only works with the buttons in momentary mode and MIDI2LR does not send an update to the controller,
for this reason the button has to be pressed twice to register a change in MIDI2LR.
All this information can be found in the
Wiki and by studying the source code.
The controller update function for knobs is "reasonably" simple, the MDI2LR plugin retrieves the development settings from LR and sends all values to the MIDI2LR server. The MIDI2LR server knows what parameter has been assigned to the knobs and sends the update to the controller using the CC address in the profile.
It is important to understand that updates are only send in the develop module.
Implementing button status updates would have to be implemented for all the other modules which is a major effort.
But that also implies that MIDI2LR has to be modified to react on a state change of a button (toggle versus momentary).
All very interesting, but the real reason why it will not be implemented is that MIDI2LR supports any MIDI controller, including those that do not have LEDs or support state update using MIDI messages: implementing blinking lights brings new complexities that are not needed for use with LR. When I use LR my eyes are on the monitor and my fingers on the MIDI controller.