"Floorbest" -- what is that? 1960s apartment

for underfloor heating

Remember, underfloor heating in apartment buildings is (as of today) almost never feasible.

Ok, thanks, it seems to me that if I want to know exactly, I (or a specialist) will have to take a sample.

Remember, underfloor heating in a multi-family house is (as of today) almost never feasible.

Yes, that is rather a vague hope that in 10 or 20 years the owners' association will agree to a major renovation. If not, that's also ok.

the owners say they knew nothing about asbestos.

the asbestos-containing flooring should actually have been removed beforehand, provided the owners did everything properly, right?

Find the mistake! If you know nothing about asbestos, you will not comply with any asbestos regulations. But that does not mean it cannot be asbestos.

Remember, underfloor heating in apartment buildings is (as of today) almost never feasible.

That is more of a vague hope that the community of owners will agree to a major renovation in 10 or 20 years.

This has less to do with the more modern attitude of future owners in several years and more with the consequence of frequently changed relative heights (e.g. fall height at window sills), which are more difficult to accommodate than in single-family houses.