How to deal with increasing property tax burden?

Housing shortage and rental distress is one of the great problems of our time.

There is a relatively simple way to at least somewhat alleviate the shortage. Require all landlords with more than 20 apartments to agree to an exchange without increasing the rent. So many older people live in large apartments and would like to give them up if the smaller apartment were not then more expensive.

There is a relatively simple way to at least somewhat ease the shortage.
Oblige all apartment owners with more than 20 units to agree to an exchange without increasing the rent. So many elderly people are sitting in large apartments and would like to give them up,

Nice idea, but not effective. The elderly do not want just any apartment, but a comparably affordable apartment in the immediate vicinity.
They do not want to exchange 120 sqm for 600€ for 75 sqm for 900€ (both apartment rents remain unchanged).
Owners with more than 20 apartments are a) rare and b) even more rarely have suitable exchange apartments.
There are countless singles living in even more small apartments. They are not necessarily looking for something large. Etc.

Good idea, implementation only possible in absolute exceptions.

Nice idea, but not effective. The elderly don’t want just any apartment, but a comparably affordable apartment in the immediate vicinity. They don’t want to swap 120sqm for 600€ for 75sqm for 900€ (both apartment rents remain unchanged). Owners with more than 20 apartments are a) rare and b) even more rarely have suitable exchange apartments. There are countless singles living in even more small apartments. They don’t necessarily look for something big. Etc.

Good idea, implementation only possible in absolute exceptions.

No idea where you live. Here there are tons of residential quarters where there are small and larger apartments, which of course all have the same owner (housing company or cooperative). And there the 75 sqm apartment also costs less than the 120 sqm apartment, at least so far. Only with new rentals is a significant mark-up applied, and that’s where the whole thing fails.

No idea where you live. Here there are countless residential neighborhoods where there are small and larger apartments, all of which of course have the same owner (housing company or cooperative)

I work nationwide. Also with such companies. That is only a very small part of the housing stock. The vast majority belongs to private owners.

That is true for the overall stock (to my knowledge about 2/3 in private hands), but there is still a correlation between the regions where a large share of rental apartments are indeed in public hands or owned by private companies and regions where the housing shortage is particularly severe.
E.g. Berlin: there (as of 2019) 60% of the stock belongs to professional owners and of that 50% to private companies.
That is certainly the extreme example, but in other metropolitan areas and metro regions the trend is at least similar, especially in Hamburg and M.

In this respect, a mandatory exchange assumption without rent increase could actually make a difference there.
The problem in the recent past was more about how interested parties find each other. I think there are now many possibilities and, for example, an offer from the municipalities could help.
Is that the big gamechanger? Certainly not, but it is one adjustment wheel among many and you cannot tackle only one thing at a time. Above all, it initially costs nothing but the effort to make the law, possibly later something for the platform of the exchange market.
We also have to get going. The constant braking by naysayers harms more than progressive ideas that perhaps do not solve 100% of all problems.

The problem is that many residential buildings are also homogeneous. When I look at my portfolios, entire streets are filled with comparable apartments. Different apartment = different streets. Different streets often mean new buildings if the old apartment is an old building. Old apartment with elevator, new apartment without = next exclusion criterion. And so on. There is a reason why such swaps rarely work (even if the offer exists).