Availability control

I would like to have availability indicators (such as time last seen) grouped. Would it be possible to create a new Semantic Property called Availability ? Or is there another way to do it ?

Ideally I would like to have a color panel with the availability (battery, etc) status of selected devices.

You can use basic features such as groups and have been ever able to do so.
This is unrelated to the semantic properties in OH3.

I guess his question targets the generated tabs like Locations, Devices and Properties on the overview page.

I’m myself are clueless about how this pages fill with cards and measurements based on properties/tags of the model/item elements.

If they were defined as Semantic Property they would appear here, right ?

It would be more convenient than just defining groups.