Slimes aren't spawning in slime chunks, unless the spawning mechanics changed. I tried to build a slime farm like I did in my 1.17 survival world after I used chunk base (seed breakdown tool) to find a slime chunk. Only this time, no matter what I did, slime would never spawn. I even tried to clear out an entire chunk, to no avail. I verified the chunk was a slime chunk through super-flat where slime did spawn, but in my normal snapshot 21w43a survival world, I have yet to see a single slime spawn.