[b3orn]

> I also learned from him that a lot German nuclear facilities are still running there generators only as weight to stabilize the network

The term for this is synchronous condenser. According to the system stability report 2023 [0] there were three of these in Germany in 2023 (source is in german, the term you're looking for is rotierender Phasenschieber). It is not clear if these are converted generators, most likely they are not former nuclear power plants, but likely located at the sites of former coal power plants because of the existing grid nodes. For the future this is a concept that is investigated to provide reactive power, in that case from former coal power plants.

[0]: https://www.bundesnetzagentur.de/DE/Fachthemen/Elektrizitaet...