Despite the controversy around X of late, It appears that most charities have remained on the platform, although some have also taken steps onto new platforms such as BlueSky.
A recent edition of Civil Society News signposted a blog which provides an in-depth analysis and some useful case studies, and you can read it at https://madlinblog.wordpress.com/2025/05/22/the-growth-of-uk-charity-bluesky-may-2025/ (we have no control of external links).
If you are leading a discussion on the social platforms that are right for your organisation, this should help you.