Summary:
https://www.minecraft.net/article/minecraft-1-20-5-pre-release-1

OOZING

• Will only spawn slimes in a given 5x5x5 area up to the max entity cramming count

maxentityCramming set to 0 prevents slime spawning from oozing effect. This is contrary to the maxentityCramming rule - when setting this rule to 0, this rule is "disabled" (mobs will not take damage from overflow at all), similarly, the restriction on slime spawning should also be disabled when maxentityCramming = 0.
This also makes the oozing effect useless for players who like to play with maxentityCramming = 0.

Steps to reproduce:

1. /gamerule maxEntityCramming 0
   

1. /summon minecraft:zombie ~ ~ ~ {Health:0f,active_effects:[{id:"minecraft:oozing",amplifier:0b,duration:-1}]} 

Observed results:
When maxentityCramming = 0, slimes will not spawn.

Expected results:
When maxentityCramming = 0, slimes will spawn without restrictions.