Mobs loaded from structure blocks ignore /gamerule doMobSpawning false
Steps to Reproduce:
1. Load a world with /gamerule doMobSpawning set to false
2. Locate a structure that generates mobs upon generation (ex. Woodland Mansion)
❌ Notice the mobs still spawn
I was able to reporduce. It seems mobs loaded from Structure Blocks aren't affected by the rule. I've reworked your report to reflect that.