Hey GoatzZ512!
Indeed, this is a known bug with ArrowDMG in Wurst 7.43 / Minecraft 1.21. We're tracking this issue in Wurst-Imperium/Wurst71010 and a partial fix is planned for Wurst 7.44.
By "partial fix", I mean that the new version will work again, but sadly it won't do quite as much damage as it used to do in older Minecraft versions.