U created a mob farm for spiders useing magma and hoppers, but I have a center point where if I stand and punch spiders, xp will drop. I was wondering if it is possible to get it so if a mob dies on magma, it still drops xp. If this is a bug, pls let me know.
This is an intended feature. Mobs only drop experience when they die due to a player or have recently taken damage from a player, including player lit tnt and fall damage from being pushed off by a player. Natural damage such as normal falling, cacti, drowning, fire, suffocation, or magma blocks will not cause experience to be dropped. If you deal damage to the mob near its death, such as you punching them, they will drop experience regardless of how they die as long as they die soon.
Be prepared to be bored. A single spawner will only ever generate 4 mobs at a time at its fastest and the spawn delay ranges from 10 to 45 seconds, so just to keep you busy the entire time you'd probably need an absolute minimum of 3 cages and probably a practical minimum of 4.
Similarly, any one cage can only have up to 6 mobs of its spawning type anywhere in a 9x9x9 area (in other words, within 4 blocks of the cage in all directions). It doesn't matter how the mobs were spawned, so if the cages were too close to each other mobs from one cage could disable another cage if both cages were the same mob-type. Generally you will have the opposite problem, though, in that the cages are too far away that you can only activate them in turns which puts you back to the 4 mobs at a time rate.
If you meant the darkroom spawners that don't involve cage spawners, go ham. Just be aware that transporting them too far will take too long and will impact spawn rates downward, so as fun as running around killing mobs dropping in with a mostly-even density it will probably still be a fair bit underwhelming.