The darkness effect has been updated in the latest 1.19.0 beta/preview, however, the darkness effect seems to show up abruptly instead of coming in from afar to the players.
This is different from Java, where the darkness effect will come from afar to the players.

How to Reproduce
1. Step on a sculk shrieker to trigger the darkness effect, or summon a warden.

Observed Result
The darkness effect comes in abruptly.

Expected Result
The darkness effect should come in from afar to the player.