After defeating a pillager captain, the player does not obtain bad omen. This means players are unable to starts raids as captains are the only way they can obtain bad omen. Via commands it is still possible, but not through killing captains.
Steps to reproduce
1. Open Unable to obtain bad omen.mcworld
2. Press the button to summon a pillager captain
3. Kill the captain
The player obtains bad omen after defeating the pillager captain
The player does not obtain bad omen after defeating the pillager captain.
See here a demonstration video of the bug. The bug has also been confirmed in infinite worlds where pillagers spawn inside the pillager outpost. Captains don't give bad omen when defeated.mp4