No true scotsman's fallacy - no serious person would use X; if you use X you aren't serious.
For example there are emergency systems or local governments that announce information on Twitter. These feel like serious organizations to me. At minimum I feel like they should be in multiple places and not just Twitter.
A few weeks ago when there was the pacific earthquake, I had family who were very close to a danger zone vacationing. Google was not sufficient for finding good local timely info as an outsider but twitter was.
I would never even think to check BlueSky or Mastodon, and my family will never have heard of them.