The EU itself also has a Mastodon instance with the funny, overly clear name of social.network.europa.eu

But only the institution of EU, not for EU residents.

I like this idea because it becomes very easy to verify authenticity especially now that verification badges on X is just subscription badges without verification. You simply set up a subdomain of the form social.country.tld and you’ll know forename.surname@social.country.tld is an authentic representative for a political party or whatever. No money involved other than running the instance, which will be a tiny cost for something as niche as one offering a voice for the parliament.