So how do you get that data (status) now (if(is-critical-peak-event){})? Do the smartplugs gather some smartgrid-style data?

It depends on your supplier, because they set the pricing and that information gets displayed on your meter. Octopus (UK) has a dynamically-priced service called Agile where you can query the API as a user; in some cases the API doesn't even need a login for regional pricing. You would have to build some logic on top for most smartplugs through something like HomeAssistant. There are storage batteries which can react to pricing, and some which will also work in concert with current solar power or other renewables.

https://octopus.energy/blog/agile-smart-home-diy/

https://www.zerofy.net/2024/03/26/meter-data.html for some more European info on meters, though mostly focused on accessing your own usage data.

I do believe I've seen some plugs that do connect to some data source to do it automatically, but I'd rather not give plugs access to the internet haha. Our provider also gives advanced notice via text or email so its totally possible to connect it up yourself.