First, if demand is not there, installed capacity isn't fully utilized. Since production costs of existing renewable installations is lower than carbon-based plants, a lull in demand will automatically increase the renewable percentage, that's neither good nor bad. But in fact, installed capacity is rising: https://www.umweltbundesamt.de/bild/installierte-leistung-zu..., so no, the record is not only due to lower production.

Second, until 2022, renewables were actively hindered by the various Merkel cabinets. The roadmap going forward is way more aggressive, but of course planning takes some time. So a "rapid build-up" is still a multi-year thing.