How do I update multiple records using `update_recordset` in X++?

Use update_recordset when the update can be done as a set instead of row by row.

SalesTable salesTable;

ttsBegin;

update_recordset salesTable
    setting YourCustomField = NoYes::Yes
    where salesTable.CustAccount == 'US-001';

ttsCommit;

For a simple bulk update, this is usually much better than looping through thousands of records and calling update() one at a time.

Just remember that set-based operations can fall back to row-by-row behavior depending on table logic, so do not assume every update_recordset is automatically one SQL statement.