Welcome! 
Device Type Handlers written in the Groovy programming language are part of the old architecture. They are still available but due to be discontinued at the end of September. So at this point it’s best to just start with the new architecture, Edge Drivers, as @Mariano_Colmenarejo suggested.
If you want to read more details about this transition, see the community FAQ:
FAQ: I have no idea what Edge is. Is that a new developer tool? (2022)
JOINING A NEW NETWORK
As far as your current issue, it’s very likely that you need to clear out the old network information from each device before it will accept being added to a new hub. In zwave, this process is called “exclusion.” It is different from just “resetting” the device. If you don’t have access to the original hub, that’s fine: zwave has a special utility called “general exclusion” which allows ANY certified zwave hub to issue an exclusion command to ANY certified zwave device even if they were never on the same network before.
It is likely that your new ST hub can’t find your Fibaro devices because your Fibaro devices think they still belong to their old network, so they are not responding to the scan. Only devices that are available to join a new network show up in the scan list. A general exclusion will clear out the old network information, so then the device should show up in the scan as available.
I am tired today so I will leave it to others to help you with the details. But your next step should be to issue a “general exclusion” to each of your Fibaro devices to get them ready to join a new network.