Desired financing possible despite Federal Financial Supervisory Authority hammer, 0 KfW funding, etc.?

Can we please continue to be upset that 5€ per month has been allocated here for clothes (if at all, maybe the Schiesser fine ribbed underwear will last until after retirement. Or you just join a nudist club), and people have children or don't have children the way they envision it? We are no longer in the age of the pyres.

I personally consider your expenses to be too general and set too low. For car costs, you only consider the current expenses but do not build up a reserve for a new (used) car if the current one breaks down. 20 euros per month for repairs amount to 240 euros per year – the pure maintenance service and the TÜV every two years already cost more than that. And that's without any actual repairs or replacing wear parts like tires or brakes.

The 10 euros for a future RLV are also too low – for that amount, you only get a 100K insurance sum. Also, check your leisure expenses...

What I think is good: your plan to save 2,500 euros every month. Try to really stick to that consistently. There will be months when it is easier for you than others. Don’t get discouraged by that and try to keep it up anyway, and at the same time, keep a household budget book.

and simultaneously keeps a household budget book.

That’s always a good idea.
I’m too lazy to keep a proper one where I have to record every coffee I buy. I made myself a big Excel wallpaper.
At the top is what comes in monthly. Below that are the fixed costs for house & living. Then below that the fixed costs for contracts.
Then there are some fixed costs for insurances and leisure. I used to have a section for liabilities (smaller loans or something). Then another section for savings rates/reserves.
And below that I have a section where I accept flat rates for the variable monthly costs: groceries/drugstore, cash, gasoline, clothing. These are just estimates that I calculate every month with the same amounts.

At the very bottom of the wallpaper I offset the balances against each other, then I arrive at a "result after fixed costs" and a "result" (the variable ones are also deducted there). And that way I know on average what we have left at the end of the month.
Sometimes it matches better, sometimes worse – you don’t buy clothes every month, for example. But it’s a great overview and I work a lot with the table. For example, I also mark every month in green what has already been debited. Then when you look at the account balance you always know whether most of it has already been paid, or whether someone still debits a larger chunk.