I use saved toolbars primarily for easily getting items that are not in the creative inventory, stuff like command blocks and the structure block. I have already gotten all of the default items like that, and now I am trying to get items that would take up a lot more space, specifically mob variant spawn eggs and all of the mob spawners. My current setup involves placing all of these into shulker boxes and then saving those, or shulker boxes in chests if I really need more space. However this is really inconvenient for quick access, and I would only really use these items if I need to use them a lot.
So is there any way to add more toolbars without modding the game? I already tried myself, but it seems impossible without mods.