Summary:
Explosions (TNT, end crystals, creepers...) do not push the Warden.
Steps to reproduce:
Summon a Warden.
Create an explosion near him.
Observed results:
Warden is not knocked back by explosions.
Expected results:
Warden will be knocked back from the explosions.
Linked issues
Comments

Does this issue apply to golem, ravager, and other mobs that are immune to knockback?

The warden is the strongest tank mob in Minecraft, I'm not surprised he's immune to explosion knockback
The iron golem also breaks parity in this case (can't be knocked back), but not the ravager - it gets knocked back. If this is intended by gameplay, Mojang will resolve this report as WAI and it will have to be added to Java.

relates to MCPE-43662.

Seems like all mobs that are completely knockback resistant in bedrock just don't get knocked back by explosions. Wardens and Iron golems are completely knockback resistant, so they take no knockback from explosions, whereas hoglins and ravagers arent, so they still take a bit of knockback from explosions.
Still affects 1.21.43
At the very least this is a parity issue, since in Java explosions can knockback Wardens. And iron golems can also be knocked back.