Hi,
I’d agree that input S2 of a Fibaro FGD-212 could be wired to a momentary push button and programmed to trigger speech or audio as a door bell, this is likely to be dangerous.
Fibaro dimmers typically use a simple capacitive dropper power supply which means it is not isolated from the mains.
As @mstormi says, doorbells use an unregulated but fully isolated transformer providing 8-12V AC. This means bell push switches are simple mechanical designs without the insulation and waterproofing needed to protect a visitor from 220-250V AC mains voltage.
Whilst you could rig up something like a 6-12v relay to provide some isolation between the LV bell supply and HV dimmer, I’d suggest it’s simpler to try something like…
The script for the door bell is the easy bit - playSound(“doorbell.mp3”) , add speech, or even send an email complete with an attached web cam image of the visitor.