Mob spawners emit light level of 3 on bedrock, but emit a light level of 0 on Java edition. With the proposed change that mobs only spawn in complete darkness, the light level will block spawn spots and reduce rates on mob spawner based farms. A proposed solution would be to make mob spawners emit a light level of 0.
Included in patch notes of 1.17.30.21 Beta, will need to test to ensure it is fixed.