Always check terms and privacy policy before signing up, but these seem like they will be here to stay:

• lemmy.cafe
• sopuli.xyz
• slrpnk.net
• lemmy.dbzer0.com
• anarchist.nexus
• scribe.disroot.org

Those are all Lemmy and PieFed, and I’m not so familiar with Mastodon and others. Maybe look at mas.to ?