With your equity, you initially get reasonable offers, so Riester is currently not necessary. The disadvantages have been presented. In particular, using it for the residual debt after the end of the fixed interest period I consider an interesting option.
Regarding your other question: You have the choice to either terminate the contract and receive the value of the funds paid out, or you continue the contract regularly and have a partial amount paid out (at least €3000 must remain in the contract).
Thirdly, you can put the contract on hold in the second option and from then on make your Riester payments on the loan. For these payments, you will continue to receive the Riester premiums, but the housing promotion account will also increase accordingly.
Since you are still far from retirement, with 2%/year a few euros of "interest" already add up for taxation (taxation always occurs only at retirement, either all at once with a discount or annually proportionally).
So käme man aus einem ziemlich renditeschwachen Produkt wieder sinnvoll raus.
However, I disagree, at least when it comes to fund savings plans. My contract currently has >30k with just under 20k in contributions, and the tax refunds have not even been factored in yet.