Renewable-heavy grids like Germany use overlapping layers of protection for this sort of thing.

Tier 1 is flywheels because they have the fastest response, and then response isn't regulated by software but instead is purely mechanical

Tier 2 is batteries, they can be made to respond to current or frequency faults in a response time on the order of miliseconds, and the flywheels give you plenty more time than that to make grid-wide orders for the batteries to respond

Tier 3 is gas peaker plants. The batteries are able to buy enough time that if there's a serious fault that could last multiple hours, you're able to spin up (or down) a gas peaker plant to adjust the grid frequency / current.