This is a challenge datapack.

The actual task/challenge is up to you, could be beating the dragon, could be completing all the advancements, or anything else you come up with.
This datapack adds an extra layer of difficulty to your task, you're allowed to only use the 9 hotbar slots, and the offhand, the other inventory slots are all blocked.

Mechanics:

• If you atempt to place an item in one of those blocked slots it will be dropped at your feet and the barrier will immediately get placed back, so if you accidentally place an item there you're not going to lose it, well.. unless you're somewhere above lava or other tricky situation like that.
• If dropped on the ground the barrier blocks will be deleted
• If moving the barriers to hotbar or offhand will also remove them
• Creative mode disables all the autoreplacing of items in inventory (will not refill with barrier blocks in the inventory and will not remove the barrier blocks from the hotbar)

Tested for 1.17 - 1.17.1
*due to changes in 1.17 to the commands ('replaceitem' command becoming 'item replace') this has to be a separate datapack from the older versions, you can find the datapack for 1.16 at: www.planetminecraft.com/data-pack/hotbar-challenge-5301608/