Buy property with own funds or with a mortgage (loan)?

Here is my answer again:

I haven't calculated it thoroughly, but overall it sounds plausible at least for the first few years or for a bullet loan.

From a purely tax perspective, your statement should be correct.
Prerequisite: the interest is fully deductible (topic discounted rent to relatives).

But as GeorgPutz already said:
To be able to assess this from a business perspective, you have to consider it as a whole and not just now, but over the entire period.

the apartment is not rented out at a reduced price.

as I said, exactly this business administration aspect should not be the question here. I have already thought about all that. it is purely about the financing.

then I apparently do not have a misconception. now I really just need a simple calculator that takes the interest rate into account at different loan-to-value ratios.

Does anyone have a tip where I can find such a small calculator?