Allay silverfish slime farm

A slime farm that needs no slime chunk, no swamp and no spawning at all. Allays are parked on soul campfires, where fire damage is slower than their own regeneration so they never die, and a splash Potion of Infestation makes every few points of that damage spawn a silverfish. A splash Potion of Oozing on the silverfish means each one leaves slimes behind when it dies, and crafters turn the slimeballs into blocks on the way to storage. It runs on potions rather than on mob spawning, so it is not really a farm you build and leave, it is one you keep stocked. Armadillos work in place of allays and several builders prefer them.

Put the campfire out when you finish using it. Allays take damage ticks as the chunk loads and unloads before they can heal, and that is why people come back to find them all gone.
Armadillos work instead of allays, breed more easily and do not make the screeching noise.
Do not use stone bricks anywhere the silverfish can reach, they infest them. The video only mentions this at 8:37, most of the way through the build.
24 mobs is the limit. Past that entity cramming kills them.
If the infestation potion is not firing, wait for the hopper timer or just splash one by hand near the allays so it is not wasted.
Java only. The creator says so at 18:04 and several builders had finished the whole thing by then.