I can't use the backpack feature in vr because it not keybinded and I can't use the steamvr keybinding becauses it not in there

The GitHub is not for support, head to the Discord for that.

That said, if you read the wiki for the Bag https://immersivemcwiki.hammy275.com/vr/bag.html , it mentions how you should bind it to the radial menu. Do that to access the bag.