The end of light mob farm involves 2 key components - update suppressors and light suppressors using an update suppressor to prevent the portals from updating when the side obsidian blocks are removed. This creates a sliced portal in which mobs can spawn where the light level is 0. The light suppressors allow the light levels of the portal blocks to be 0, meaning that mobs can spawn directly into the portals and get transported into a drop chute.
Update suppression is a glitch that allows the player to update certain blocks without causing updates to another. The main use is to make sliced portals which is a key component of the farm. It is used to place blocks at impossible block states usually done by stack overflow. If the update is cause directly by a player, it will not crash the game. But if it is done by natural means, it will crash the game. Using powered rails is the method of choice for most players. This does not work only in Java Edition 22w11a, when the update order was changed from a stack to a queue. The bug was fixed in the next snapshot, 22w12a.