Use Riester pension for financing?

Nonsense. Then I only produced costs and lost even more money

Before dismissing it as nonsense, please take a look at the corresponding calculations. Something like that appeared, for example, in Wirtschaftswoche. That is very plausible because the subsidies & tax savings could still work for you, and this way you avoid the pension catastrophe.

Good question, I ask myself that all the time too. They are really two different things: On the one hand, for someone without Riester the question is whether to sign up. On the other hand, for someone with Riester the question is whether to keep/cancel/put on paid-up status? A good part of the costs is paid AFAIK in the first years after signing the contract. If the contract is already running, it might be better just to hold out.

You usually only have these high initial costs with insurance products. But not, for example, with a unit-linked variant. The biggest problem lies with the pension phase; that's what I’m trying to explain here all along.

By the way, I continue to fund my Riester contract because of longevity risk. Maybe I'll live to 110 after all, then it will have been worth it. Besides, you also need more defensive investments in your portfolio; so I just aim for more return with other things.