According to [1], 3/4 came from renewables during the re-startup. Most of today's inverters are black-start ready. That is, they don't require external energy to startup, unlike nuclear, which is heavy, costly, and slow. German readers may find fefe interesting here [2]. He debunks many of these myths.
If the addition of renewables leads to an unstable grid, it is irrelevant if the grid is then restarted with the help of renewables.