I am making a mob farm on minecraft:bedrock edition and I light up ALL the caves, go 24 blocks away, and wait 30 mins but nothing spawns. I saw a youtuber make this and get a REALLY good spawn rate, but I get 0 mobs a year.(yes, it's that bad). Why does every spawner that a youtuber makes NEVER work for me?!
Tails1 is being a bit vague on this. The truth is that there are a number of bugs that are effecting bedrock edition in respects to mob spawning. If the area around you is relatively lit up and mob spawn proff, in time your farm should work once these bugs are worked out. I just wouldn't hold my breath waiting.
In respects to mob farms that work on java edition, most should work on bedrock edition as long as the java edition doesn't use quasi-connectivity in any of the redstone that the farm might use, and if it does, there are ways around that as well, but getting off topic.