The shield doesn't take damage or lose durability and you don't get knocked back by exploding TNT or creepers.
When you are hit by other mobs you lose durability, but this does not happen in the face of explosions, that is, it does not lose durability and it does not push you almost anything back
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We're tracking this issue in MCPE-121484, so this ticket is being resolved and linked as a duplicate.
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