Sorry, I’m confused by your question.
First, the Fibaro dimmer and the Fibaro relay (switch) Are two different devices. The relay does not dim at all, it’s Just a binary on/off switch.
Second, By definition, “momentary” switches don’t latch into the typical two positions of a regular (bi-stable) switch. They work more like a traditional doorbell switch where they rest in the off position and only turn on when you press them, then automatically return to the off position.
A momentary switch that looks like a rocker commonly has three positions, not two: press on the top, press on the bottom, rest in the middle. This is the kind that most people would use so that when you press on the top like it brighter and when you press on the bottom, it gets dimmer.
So can you give us a few more details of which Fibaro model you are using and what you are looking for and then hopefully we can help with suggestions.