Don’t know who exactly you are interested in, here are some random known accounts:

• the EU commission (other EU institutions as well): https://ec.social-network.europa.eu/@EUCommission
• gog games: https://mastodon.world/@goggames
• The New Stack: https://hachyderm.io/@TheNewStack
• Mozilla: https://mozilla.social/@mozilla
• Rust foundation: https://social.rust-lang.org/@rust
• Free Software Foundation: https://hostux.social/@fsf
• Electronic Frontier Foundation: https://mastodon.social/@eff
• Greta Thunberg: https://mastodon.nu/@gretathunberg

Regarding individuals, I’m following a bunch of software developpers. I’m mostly interested in topics, hence I prefer Lemmy by far.

Mattermost used to be the go-to alternative, not sure why it is not mentioned yet. Then it looks like Revolt is getting traction now.