Raid captains, found in pillager patrols, should impart the Bad Omen effect when killed by the player. However, if the captain is killed by shooting the player & taking damage via the thorns armor enchantment, the player does not receive any effect.
Resolved at some point during or before 1.18.31.
Confirmed. I have experienced this multiple times myself in 1.14 versions on Windows 10, and it was not what I expected.