In previous versions of Minecraft, using multiple Blast Protection enchantments caused no stacking effect. In 1.21+ the enchantments stack and cause people to take absolutely no explosion knockback.
Steps to reproduce:
Enchant multiple Netherite gear with Blast Protection IV (e.g chest/leggings)
TNT or end crystal
Observe there is no knockback
While this may be expected behaviour it certainly does not feel so.
Thank you for your report!
However, this issue is Working as Intended.
The report you have submitted is working as intended: the 1.21-rc1 changelog mentions the following:
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