Exist an attribute for cataloguing empty houses or flats?

The usual way to mark this in OSM is with disused=yes. From the wiki page

A disused feature is any man-made feature which is no longer used for its intended purpose, but which is still maintained and has repairs made. Reuse may be planned. Disused features are still useful for navigation and are visible in the landscape. Frequently these will be boarded-up buildings; for example, an old disused multi-storey car park.

So this seems to fit your case quite well. Note that in addition to adding this tag, you should change any tags which no longer apply, by prefixing "disused:". For example amenity=pub becomse disused:amenity=pub, because the building in question no longer houses a pub. This is important for software which does not understand the disused tag - otherwise it would see the amenity=pub and list it is a pub.

So in your case you could just add disused=yes to the abandoned buildings. In that case, I don't think it's necessary to change the building=yes (or building=residential etc.) tag - the building is still a building.

taginfo reports building=abandoned which you could use for this. There is also building=disused but the meaning seems not very clear to me.

Furthermore the wiki suggests that you can use any tags you like. But note that not every information belongs into OSM's database. For personal purposes better create a separate database and display its content via an overlay on top of a OSM map.