Here are the highlights:

• Production Taproot Channels — Finalized simple taproot channels (feature bits 80/81) are now supported, using optimized scripts and map-based nonce encoding. Open explicitly with --channel_type=taproot.
• Onion Messaging Forwarding — Basic support for relaying onion messages, including pathfinding via the channel graph and rate limiting with per-peer and global token-bucket limiters.
• RBF Cooperative Close for Taproot — The RBF-based cooperative close protocol now works with taproot channels, including MuSig2 partial signatures with just-in-time nonce patterns.
• Reorg Protection for Channel Closes — Channel closes now require 3–6 confirmations (scaled by capacity; wumbo always requires 6), making them reorg-safe.
• Fast Neutrino Initial Sync — Neutrino nodes can bootstrap block/filter headers from a local file or HTTP(S) URL, reducing fresh sync from hours to minutes.
• Native SQL Payment Migration — The KV-to-SQL payment store migration is now promoted to production code (enabled with --db.use-native-sql).
• Database Network Guard — Prevents silent data corruption by refusing to start if the database was created on a different Bitcoin network.
• Removed Deprecated Payment RPCs — SendPayment, SendToRoute, TrackPayment, and the outgoing_chan_id field are removed. Migrate to the V2 equivalents.
• Removed Tor v2 Support — --tor.v2 flag removed; v2 .onion addresses are rejected at the boundary everywhere.
• MinCLTVDelta Increased to 24 — Raised from 18 for a larger safety margin above the default final CLTV reject delta.
• Database Performance — Asynchronous graph cache loading, cursor-based invoice pagination, optimized HTLC settlement queries, and tombstoned (rather than cascading-delete) channel closes on SQL backends.

Full release notes https://github.com/lightningnetwork/lnd/blob/v0.21.1-beta/docs/release-notes/release-notes-0.21.1.md