Summary (related from MC-270099)
The mobGriefing game rule disables most mobs from placing or changing blocks. However, the new Weaving effect does not check this game rule. This also effects Bedrock Edition, hence the bug is able to be reproduced here.

Steps to Reproduce

1. Create a world with Update 1.21 experiments enabled.
2. Run /gamerule mobgriefing false
3. Summon a mob.
4. Apply the Weaving status effect to them.
5. Kill the mob.

Expected Result
No cobwebs are placed.

Observed Result
Cobwebs are placed.