switch_dimmer, should control the root control - normally this is mapped to endpoint 1 which is why you see switch_dimmer 1 also moving when you move switch_dimmer.
switch_dimmer1 is the first endpoint - the reason you don’t see switch_dimmer change here is because this is now using multi_instance messaging, so switch_dimmer = switch_dimmer1, but switch_dimmer1 != switch_dimmer (if that makes sense?!?).
switch_dimmer2 should be the second switch. In the FGD212 there is no load connected to this, but you can use the button on the device to send messages - effectively using this to control a completely different switch.
We probably should delete switch_dimmer from the channels list in the database, but these are generated automatically in the database until someone with more knowledge of the device goes and edits it. By that I mean that the database software can’t automatically know what all the connections are, so it just provides everything until it’s manually updated.
I hope that makes sense anyway? 