FYI new Twitter migrants, if you just want to browse, try these.

General:
https://mastodon.social/explore
https://mastodon.online/explore
https://mas.to/explore
https://mstdn.social/explore

Specific:
https://masthead.social/explore
https://journa.host/explore
https://newsie.social/explore
https://infosec.exchange/explore
https://sciencemastodon.com/explore
https://med-mastodon.com/explore
https://sciences.social/explore
https://econtwitter.net/explore

There's a lot of overlap in posts they're showing, but they're not exactly the same—that's the nature of federation.