How do I delete multiple records using `delete_from` in X++?

Use delete_from for a set-based delete.

MyTable myTable;

ttsBegin;

delete_from myTable
    where myTable.Processed == NoYes::Yes;

ttsCommit;

It is fast when the table supports set-based deletion, but be careful with delete actions, overridden table logic, and related records. Do not use it just because it is shorter.