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You are thinking way too complicated ;)

if you don’t want to pay any closing fee for the home savings contract etc., and possibly after that another discount.

I would do it completely differently:
Take the 120,000€ from KFW in the normal way, once it is renovated, there is a repayment grant of 42,000€
if you pay 400-500€ monthly, the remaining debt after 10 years is manageable, so 25,000-35,000€, depending on circumstances you could have saved that amount by then. So this part can be completely paid off in 10 years. No annoying closing costs for the home savings contract etc.

I would do the rest over 20 years, with a monthly payment of 250-350€ + BUT 5% prepayment option. That is 4000€ per year. You wouldn’t use that at all in the first 10 years, but start using it from the 11th year (KfW is gone!), and thus have the loan paid off in 20 years.

In the optimal case, you get a repayment switch included for the 80,000€, then you can increase the rate + prepayment.

In the end, make an Excel sheet with the costs like interest, closing fees etc. and calculate several models. Where I end up paying the least for the 200,000€, with a 750€ monthly burden, I simply choose that...

At the end of the day, if you manage to make a 2500€ prepayment every year in the first 10 years or save that money, then you can also repay the 200,000€ in 18-19 years!

Under no circumstances would I personally even consider financing at over 2% interest with the loan-to-value ratio. Overall, I see it rather at 1%

Hyponex described it well, I don’t understand why you keep ending up with [Bausparvertrags-Varianten].

I would do the rest over 20 years, with a monthly rate of €250-350 + BUT 5% special repayment option. That’s €4000 per year. You wouldn’t use that at all in the first 10 years, but from the 11th year on (KfW is gone!) and thus have the loan paid off in 20 years.

Why would you repay the KfW at 0.75% first, and only later the other? Wouldn’t it make more sense to put extra money into the more expensive loan instead of paying off the KfW?

I would do it like Hyponex, because you can usually only fix the KfW for 10 years and agree the rest as an annuity loan over 20 years. Who knows what will happen in 10 years. And, regarding the security, the interest rate for the 20-year annuity should not be significantly higher than to do it the other way around.

Well, especially the special repayments on the more expensive loan save the most money in the first years. I also consider not repaying the KfW at all to be unfavorable in an owner-occupied property.