Slimes are supposed to spawn in swamps in light levels 0-7.
However, in version 1.19.81 as well as 1.20.0.22 Preview, slimes only appear to spawn in swamps with a block light level of 0, and don't spawn with block light levels 1-7.
Please find attached a world that demonstrates the issue.
If you remove the lights, slimes will spawn properly. With the lights, slimes won't spawn.
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After some testing in v1.20.15, it appears slimes currently can spawn in light levels 1-7.
However, there are a few issues:
Slime spawning in swamps seems extremely slow. Even on full moon nights.
Slimes appear unable to spawn inside blocks that normally don't block spawning, such as redstone torches and glow lichen. They are however able to spawn inside of brown mushrooms.
All of this is much easier to test in mangrove swamps, where slime spawns at a much higher frequency (probably due to the bug that prevents other mobs from spawning in that biome).
Can confirm, with the exception that they don't spawn even at light level 0 for me. Haven't seen a single slime for a while, and even an automated slime farm doesn't produce anything.