Unexpected sale of rented apartment. Options?

Apartment search Move is too much for you now, the apartment fits, would buy

Our current apartment is ideally located both in terms of commuting and shopping and leisure value.

buy, for me this is a better investment than a number on a bank or ETF paper

Thanks first of all. Those were also our first thoughts. But the first thoughts don’t have to be right…

If we didn’t want to buy, we would get the proper termination with a 6-month notice period in our case, and the sale would follow.

The price worries me. Not because we couldn’t afford it, but because the difference to the bank’s valuation could be so large that a loss occurs in the short time until the planned next purchase (or am I making a mistake here?).

I wouldn't necessarily buy. Depending on the price, it can really cost a lot of money. The additional purchase costs are simply high. With luck, there might be a break-even point if the value increases. Renting elsewhere doesn't necessarily have to be complicated. Hire a broker for the search and let a moving company do everything. That also costs money, but you don't commit yourself. And 4 years is not a temporary phase. A temporary phase is a few months.

1. Purchase does not break the lease
2a. When did the conversion into condominiums take place? Does the landlord own the entire building?
2b. Termination for personal use is possible, provided the conversion took place before your lease began, but with relatively long notice periods
2c. Termination for personal use is impossible (blocking period), provided the division into condominiums only took place now
3. The property is already quite old. How do the maintenance reserves look? Condition of the entire building ==> possibly a new heating system is due or the roof needs to be done. People like to get rid of an apartment or the entire building because of that.

If we didn’t want to buy, we would get the proper 6-month notice in our case, and the sale would follow afterwards.

That’s how I would do it too – even if it sucks, but an unrented apartment sells better. Especially given the high purchase price demand.
BUT: How should a regular termination be justified? A proper termination by the landlord is legally excluded!

Despite the prime location, I would think very carefully about it. After all, you are tying yourselves to – according to your statements – an apartment that is too expensive. And who knows what kind of renovation frenzy awaits in the owner’s association over the next few years.

I had written further above that termination due to personal use is not that difficult, but as just described, it may not be used. So the seller may not state the sale as their personal use! Only the buyer may do so, but they must move in themselves or let a close relative move in.