How to cancel Wohn-Riester for a home or how to proceed?

I have checked. In recent years something between 650 to 700 euros was declared in the tax return, or it says there: Tax reduction related to the [Altersvorsorgezulage]... So does that mean I have to pay back this 700 € annually? Or also again a % of it

That is stated on the income tax assessment. Yes, if there was a 700.-- tax saving, you have to pay it back for each year it was granted.

Here it always basically says "if you have the money from the home savings contract paid out, a housing promotion account is created". Is that really the case? I understood it as meaning that the housing promotion account is already "created" when you start saving into the thing. It simply adds up which amounts you have claimed on your taxes during the saving phase, so that these can be taxed later. This is not mentally that complicated. These savings contributions to your Riester are – even if you hadn’t saved them there – part of your income. And income must be taxed. In the case of Riester, this just means it is taxed after retirement. But you pay tax on this part of your income either way. If you cancel Riester disadvantageously, you have to repay the tax savings (which is deducted from the payout sum). If you use it for building, at retirement through the housing promotion account.