bitcoin/doc/release-notes-pr13033.md

Transaction index changes

The transaction index is now built separately from the main node procedure, meaning the -txindex flag can be toggled without a full reindex. If bitcoind is run with -txindex on a node that is already partially or fully synced without one, the transaction index will be built in the background and become available once caught up. When switching from running -txindex to running without the flag, the transaction index database will not be deleted automatically, meaning it could be turned back on at a later time without a full resync.