Can only married couples apply for financing together?

We have different backgrounds:

Part 1 is employed and Part 2 is self-employed. Part 1 would probably get the desired loan alone. With the broker, including Part 2 as the second borrower led to worse interest rates because self-employment was penalized. Actually a joke, since the bank actually has more collateral with two borrowers.

Anyway, regardless of that, we are getting married soon. Therefore, the question now is whether Part 1 can still take out the loan alone then? The property and equity being used already belong to Part 1 anyway.

Does anyone have any knowledge about this? Would a marriage contract change anything?

Of course, Part 1 can take out a loan on their own. What kind of question is that? He is also allowed to buy a car on his own.

Of course, Part 1 can take out a loan alone. What kind of question is that? He is also allowed to buy a car alone.

Statement of the broker: with married couples, banks usually insist on the spouse as the second borrower.

Against this background, the question seems quite justified to me. I just want to know if this is (generally) how it is, as presented by the broker.

Since Part 1 also owns the property, it should be possible without any problems for Part 1 to take the loan alone...

Against this background, the question seems quite justified to me. I just want to know if it is (generally) as the broker presented it.

Generally correct. Both are employees in general, and if one should fail to make the payments or is not liquid or reliable, the other is still there. For the bank, it is spread over two persons or two salaries, so the repayment of the installments is more secure if one fails.
I am not a banker, but is this called risk diversification or something like that?

I would look for another bank if they insist on such nonsense. What would the options be? 1) Part 1 "forcibly" shares his property with Part 2: who would allow themselves to be forced into something like that? or 2) Part 2 signs a loan agreement for something that is not his property: then Part 2 would be really badly advised. A pile of debt in the six-figure range but no ownership of it. Great. No, it can be said quite generally that Part 1 can take out the loan alone.