Essentially, the mob shows up in the spawner but no matter what block I place beneath it or what light level I make it the mob just spins and spins.

Max Upgraded Spawner, with 5 Min to 10 Max Spawn Delay. On a skyblock, way under mob cap.

Minecraft: 1.16.5
Latest Version

You might need to use the Dragon Egg(?) to disable all spawn conditions. The mob just spinning usually means one of the spawn conditions isn't being met.

We need a tooltip that can show up with The One Probe that shows what the spawn conditions are.
Just like crouch to see:
Dark: Yes/No
Block: Grass/Any/Etc...
Biome: Any/Etc...

I literally could not provide that if I wanted to.

Anyway, its probably just the spawn conditions of the entity, as thats how the spawner works.