Describe the bug
subj

• Minecraft: 1.21.1
• Mystical Agriculture: MysticalAgriculture-1.21.1-8.0.19.jar
• Singleplayer or Multiplayer: Singleplayer

Not durability, damage value is like from bare hand. Another mod? Hardly, but surprisingly you was right, there is no bug without other mods. I will search a culprit...

The problem is in compatibility with mod Psi
Reported to other side:
VazkiiMods/Psi#842

Can you elaborate? If you're referring to the durability it's because the are unbreakable. If you mean the swords do 0 damage it may be a thing caused by another mod or a change in whatever modpack you may be playing.