When we first setup the server with Better MC 3 (for 1.19.2) and installed the same for our client side, we were able to update the Backpacked config file to change it from 1 row of inventory space to ...
public static final KeyMapping.Category CATEGORY = new KeyMapping.Category(Utils.id("backpacked")); public static final KeyMapping KEY_BACKPACK = new KeyMapping("key.backpacked.open_backpack", ...