Minecraft Version
What version of Minecraft are you using? 1.19

Mod Version
What version of Simply Swords are you using? simplyswords-fabric-1.43.1-1.19.2

Describe the bug
Backslot weapons are to big, would like to know which version of SimplySwords is compatible with Backslot 1.2.8 and also has the new textures?

You would need to update your Backslot mod version to 1.2.10. They changed the way they read model data in that version. I added proper support for the updated version.