As far as I know, the power outage in Portugal and Spain did not start with renewables

It’s not like a set of bowling balls and pins, one being the initial mover and the others falling one by one.

Grids are better modelled as a system, jointly operating. Insufficient damping is the cause as per the grid operator (1).

Can be solved in multiple ways such as make it a france problem (stronger interconnects to a system with more turbines), storage, improved DC-AC transformers for small (<1MW) solar plants. (*)

Pumped storage is indeed the best known technology for grid stability, as it provides both storage, and turbines with inertia. Hard to build though, finding funding and appropriate locations.

(*) the report mentions an estimated 700MW of production auto-shutting down as grid frequency dropped. Most likely these are the inverters of small scale solar installations, which are frequency following (measure then adjust) rather than synchronizing.