Here's a Brit.
Condo(minium) is 100% AE. Kevin is right, this is a cultural thing. Living in a flat is the exception rather than the rule in the UK, and, as Kevin says, most flats tend to be rented rather than owned.
For a Versammlung of the tenants of a block of rented flats: 'residents meeting'.
In the centre of some cities, especially alongside old docks, there are now some plush blocks of flats or apartments (just a posh word for a flat), in which each individual apartment is owned by the people living in it. I can imagine that these people have meetings occasionally. Could call them: apartment owners' meetings ... or simply 'residents meeting' again, as it would go without saying that the residents were the owners of the apartments in such a building.
BTW, a building consisting of lots of flats or apartments is generally called a 'block', not a house. However, large houses, originally built many years ago for one family, do sometimes get converted into flats, so you can have a flat within a house. Where the building has been purpose built, however, it's a block.