Built 2 years ago, now an additional condominium

1. That depends on your risk appetite. Secure low returns, e.g. overnight money currently over 0.1 - 0.3% and/or make special repayments = yield 2.09% (your paid interest) vs. rental yield AFTER TAXES.

If the building with the apartment has no or hardly any reserves, it is not transferable (at most you can increase the rent). Rental defaults/ interruptions/ possibly renovations after an old tenant.

You have to decide that

2. You need to contact your bank sometime

In terms of the numbers, it is certainly feasible.

I would be wary of the time that has to be invested in managing a rental apartment. Proper handover, possibly renovation, searching for tenants, trouble caused by or with tenants, annual meetings that can be annoying. Monthly payments into the owners' communal fund, possibly renovations, possibly rent loss, termination, renovation... and all that on top of job, family, and own house. I could find a better hobby.
oops, I overlooked: You are a civil servant ;)

Duisburg North is not exactly the area where you can expect very good resale value. That increases the risk. I think this is reflected in the rental yield of about 7% (on the non-negotiated price). That is initially a decent percentage.

How can you minimize the risk? Inspect the entire house (not just the apartment). What is the condition of the basement, for example? The roof?

If it is a homeowners' association: Ask for the minutes of the last two to three owners' meetings. Were damages discussed that need to be fixed in the medium term? Are there problems or is everything fine?

Can you possibly achieve an increase in value in the apartment with small means? (Bathroom, floors, etc.).

Read up on the topic of renting out; there are good books and also good videos on YouTube, for example.

And yes, this is an investment that requires personal effort. But also one that can yield one of the highest returns on equity if done well.

In real estate, the profit lies in the choice of the property and that of the tenant. If you make the right move here, you can't lose. But if you mess it up here...

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Personally, I am a fan of as high financing as possible (100% or more) when renting out. Then pay down slowly, but have the option for special repayments in the contract.

Then I’ll also speak up again.
First of all, thanks for the input.

Yes, I am a civil servant, but I wear a uniform and am generally not underemployed in my job, and my free time is important to me.
I would estimate my risk to be within a normal range; after all, I only took out my mortgage for 10 years, but I have secured most of the remaining amount with a home savings contract.
A daily allowance account is definitely out of the question; I see it as pointless.
Paying off the house faster and saving the 2.09% interest is certainly an attractive option—where else can you still get 2% safe interest nowadays?

I will now calmly take another look at the housing market, look at various properties, and get back into the subject. About 10 years ago, I looked for a condominium and failed. Then I tried for several years with a suitable used house and ultimately ended up with a new build. The market simply had nothing or almost nothing to offer.

I think I would also do 100% financing and only pay the incidental purchase costs from my own capital, so at least I stay a bit liquid. As a civil servant, I definitely have the advantage of relatively low taxation.

I think I would also go for 100% financing and only pay the incidental purchase costs from my own capital, that way I stay at least a bit liquid. As a civil servant, I definitely have the advantage of relatively low taxation.

In any case, liquidity is more important than profitability. So it's a good plan.

What still seems unanswered to me: Why do you want to buy an apartment? What advantages do you expect from it?