Minecraft version
1.16.5
Mod version
latest (1.0.2.4)

Describe the bug
Wither storm is unable to pick up certain blocks that it should. It cannot pick up end stone, obsidian, crying obsidian, and respawn anchors

To Reproduce
Steps to reproduce the behavior:
summon wither storm in area with only these blocks
observe it not picking up anything (with f3+b you can see it try but fail as if it was bedrock), This is easiest to see in the end, but it cannot pick up these blocks in all dimensions.

Explosion Resistance

This isn't a bug, it doesn't do it in 1.16.5 as it's a new feature

Why wouldn't it be able to pick up end stone or obsidian?

Shouldn't the storm be able to pick up anything (breakable) to prevent certain structures being pretty much storm proof? Also, end stone isn't very blast resistant, it can be destroyed by a creeper explosion

This is because the 1.16.5 Wither Storm uses the ender_dragon_immune block tag to check if it can pick up certain blocks, which contains the blocks you mention. The change to use the wither_immune block tag was technically a feature and won't be backported to 1.16.5.