What would you do at the end of the fixed interest rate period 2023?

I would calmly make special repayments on the KfW loan and repay it in one go in 2023. In 2023, you can consider how to deal with the large loan. In your situation and given the interest rate situation, I wouldn't currently give any thought to refinancing. It's wasted time, since a forward is still too far away.

Why? You can always ask for interest rates

You can do anything! But the question is whether it makes sense? The OP asked how he should proceed in 4 years, which is okay.

It’s (almost) just like if I asked my wife what she wants to eat on 09/25/23 in 4 years.

You can do anything! But whether it makes sense is the question? The OP asked how he should proceed in 4 years, which is okay.

It's (almost) just like if I asked my wife what she wants to eat on 09/25/23 in 4 years.

I would calmly make special repayments on the KfW loan and pay it off in one go in 2023. In 2023, you can consider how to handle the large loan. In your situation and given the interest rate environment, I wouldn't currently worry about refinancing. It's wasted time since a forward is still too far away.

I wouldn't conclude it like that today. The loans mature at different times, everything is combined into one mortgage charge.