Can only married couples apply for financing together?

For us, in a similar constellation (a and b married, b self-employed, but: property according to the land register in a and b's names jointly) it was no problem to have the loan agreement only in a's name.

Equity was proven by a and n, about the same amount from each.

Commerzbank, 2017.

No, it cannot be generally stated that Part 1 alone takes out the loan

This is not about what options one PRINCIPALLY has, but what the bank prefers. This was told to the OP:

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

And that IS simply the case. No matter who owns the property, the bank does not care about that at all. The bank wants security.

No matter who owns the property, the bank does not care at all. The bank wants security.

The only security the bank actually has is the property, by the way. The rest is trust, which is already implied by the word credit. The bank does not care who becomes the borrower (as long as they are creditworthy); what matters is that it has access to the property.

It works. We also have it like that. A is listed alone in the land register, A alone has the loan, only A's equity has been contributed B is excluded B had to prove that the income is high enough for their own living expenses and the child's proportionate share Financed through Commerzbank in 2017

that she has access to the property.

...If the worst case occurs.

Self-employed individuals still have an insolvency risk, therefore it is not uncommon to have the property fully registered under the spouse, if possible.