In the EU the grid prioritizes frequency over voltage. If production is slightly below load, voltage is decreased, not frequency. If things go really bad and frequency drops, too, they'll fix that by running at a slighly higher frequency later. Clocks that have been fixed in the meantime require to be fixed a second time.

A deviation of 6 minutes was reached and fixed in 2018.

https://arstechnica.com/tech-policy/2018/04/european-grid-di...

I have no idea if that kind of strategy is applied elsewhere in the world.