Defense Sword Add-on 1.21+

Few people know this, but swords used to be able to block enemy attacks and even deflect projectiles in Minecraft. Unfortunately, this feature was removed, and now shields are used for protection. However, with the Defense Sword mod, you can once again restore the ability to block attacks with swords. To do this, you need to hold a sword and use Crouch.

This defense is not flawless: after a couple of hits, you will start taking damage again. It can help you deflect a stray projectile or quick attacks, but you will still need to use your combat skills properly.