I have not read the report yet, but in another thread someone gave a very plausible explanation of what happened.

The high levels of renewable energy happened to contribute to this incident, but not because of something inherent in renewable energy. All renewable energy sources are connected to the grid through inverters, and in Spain most of these inverters do not use an adequate control policy, i.e. they do not compensate the phase fluctuations of the grid, like the synchronous electromechanical generators do (i.e. they do not generate an appropriate amount of reactive power for compensation).

Technically it is easy to implement such control policies in all solid-state inverters, but it was not done in Spain because there were no incentives, i.e. there were no regulations specifying how the inverters connected to the grid should behave, otherwise than disconnecting when the frequency went outside a permissible range.

Yes, that is plausible indeed, but the problem is that there are many explanations which are plausible, but there doesn't seem to be a smoking gun.

Strange about that explanation for example is that the time correlation is backwards. First the solar generation started to drop out and only then central generator stations tripped. Also the on-going frequency oscillations had already stabilized. If it was related to frequency issues, the solar inverters would either have shut down 15 minutes earlier (while the frequency oscillations were at the peak) OR 1-2 minutes later (when power stations tripped and frequency would have dipped)