In the UK, the National Grid Operator maintains "black start" plans[0] for rebooting the entire national electrical grid from a zero power situation, and they pay individual plants to conduct annual drills. However, for obvious reasons, these plans have never been tried in anything close to real-world conditions, and it's something of an open question whether it would work.
[0] https://www.theblackoutreport.co.uk/2023/06/13/black-start/