The root cause is not known, but Spain was producing excess power (primarily solar) at the time around the disconnect. Some fluctations were seen, then supply started to disconnect from the grid in Spain, leading to sudden loss of 2.2GW of power. In Spain, automatic load shedding then happened to try to recover, but it was too little too late as neighboring countries detached from Spain to protect their own grids.
Nothing about this sounds like an issue with renewables.
Still a ways away from understanding what happened
not strictly because of wind power but few denies that wind power hasn't been a contributing factors - politically it's too sensitive so it's going to be "under investigation" for a long time. Alledgedly too little inertia / rotating power ... there is a parallel to the Australian blackout 10 years ago, where the solution was to build large batteries