As stated in the summary, Mobs still spawn in low light level areas in 1.17.30. sometimes they even spawn in well lit areas. i have included an attachment of a video where mobs are spawning in  a low light level area. the torches in the area show in the video are placed 11 blocks apart. which means even at the farthest distance between two torches the light level shouldn't be equal to zero, yet mobs still spawn in those areas.