Refinancing - Tax Consideration?

But this is about income-related expenses…, and the original poster expects a lot from the new financing (for owner-occupied houses), because interest rates are higher.
His rental interest can generally be deducted, but rent must also be taxed.

No, the term income-related expenses is correct in this context. Please note, loan interest on rented properties can be deducted as income-related expenses. Period.

Point

.. period, comma, dash, and the moon face is done: I like to be well advised and corrected…. ;)

Hypothetical case: What would it actually be like if someone took out a new loan, used part of it to pay off two smaller loans for the apartment and another part for the new project? Would one be allowed to fully, proportionally, or not at all claim the interest of the new loan as income-related expenses?

Yes yes, I know, tax advisor, but it might be that someone has already had this case...

Hypothetical case: How would it actually be if one took out a new loan, used part of it to repay two smaller loans for the apartment and another part for the new project? Would one be allowed to deduct the interest of the new loan fully, proportionally, or not at all as income-related expenses? Yeah, yeah, I know, tax advisor, but maybe someone has already encountered this case...

I would deduct the loan proportionally. Whether and how the tax office recognizes that is another matter (in this case, the assessment notice). If you read through what effort one actually has to put into a mixed-use property, I would avoid such cases under all circumstances. (different accounts, different loans, split purchase price in the notarial deed, etc.)

Hypothetical case: What would it actually be like if someone had taken out a new loan, used part of it to repay two smaller loans for the apartment, and another part for the new project? Would one be allowed to deduct the interest of the new loan fully, proportionally, or not at all as income-related expenses?

Yeah, yeah, I know tax advisor, but maybe someone has already had this case...

you will not find anyone here who publicly admits to having cheated the tax office and gives you instructions on it. A good tax advisor tells you what is possible

??? It's not about cheating. I want to know how the [FA] decided in this case. You don't always have to assume the worst, you know?