From the top of my head, there are:
City of Amsterdam https://social.amsterdam.nl/
Baden-Württemberg https://xn--baw-joa.social/
Netherlands https://social.overheid.nl/
Germany https://social.bund.de/
France https://social.numerique.gouv.fr/
EU Commission https://ec.social-network.europa.eu/
Switzerland had a pilot project, but I don't know what happened to it
I'm pretty sure there are more local governments with their own instances or plans to do it , specially after all the digital sovereignty discourse got some boost to it