You do need Knots for Datum to work. All other Start9 Bitcoin services still run fine (LND, Alby Hub, electrs, Mempool, etc.). You keep the BTC blockchain and sort of convert Core over to Knots: https://community.start9.com/t/installing-bitcoin-knots/1997/4

I used this guy’s tutorial as a guide to get Datum and CLN running with Bolt12. Too bad I can’t find him on Nostr, or I’d zap him v4v: https://youtu.be/BQ6Hax3wcY8