According to the Roblox wiki, I would just have to use
game:GetService("StarterGui"):SetCoreGuiEnabled(Enum.CoreGuiType.Backpack, false)
to unbind the Backspace (or Delete) key, among other keys. However, this does not work. Does anyone know how to do so?
Many thanks in advance!
Me.

2 comments
https://devforum.roblox.com/t/unbinding-the-backwards-key/295110
Checked it already. Isn't for my situation, sadly. :(