I'm also using enchanting infuser mod. tried a sharpness book using an anvil but still can't put it on the sword.
I am on fabric 1.21.1

I do not experience this issue with vanilla enchanting. I'm not really sure how the Enchanting Infuser mod works, but there might be an incompatibility here.

Vanilla enchanting:

I also cannot reproduce this issue with Simply Swords & Enchanting Infuser.
If you have Geckolib installed, please make sure you're running the latest version, as you might be running into this issue: Fuzss/enchantinginfuser#120

oh ok, thank you for the reply will try uninstall and install mods again. thank you again! love your mod <3