Uninstalling

Short version

Removing Adjustability never deletes or breaks an item. Items keep their active enchantments and work as usual. Their dormant enchantments just stop doing anything (they did nothing anyway) and stop showing. To remove them for good, run /adjustability flatten @a with everyone online before removing the mod.

What happens to items when the mod is gone

Dormant enchantments are stored on each item in vanilla's minecraft:custom_data component (see Where dormant enchantments are stored). Without Adjustability:

	Without flattening	After /adjustability flatten
Active enchantments	Kept, work as usual	Kept, work as usual
Dormant enchantments	Stay in the item's custom_data, invisible and inert	Gone
The item	Loads and works like any vanilla item	A plain vanilla item
Putting the mod back	The dormant enchantments are back	Nothing to bring back

Nothing is lost by skipping the flatten, and you can still decide later: reinstalling brings the dormant enchantments back, and flattening then removes them.

Flattening before you uninstall

/adjustability flatten [<targets>] (operators) removes the dormant enchantments from every item in the targets' inventories and ender chests, and says how many items it changed. Without targets it flattens your own. Enchantments a player switched off conflict with nothing, so flatten switches them back on instead of removing them.

1. Get every player online (offline players can't be reached).
2. Run /adjustability flatten @a.
3. Stop the server and remove Adjustability from the server and every client.

What flattening does not reach, because it only looks at players:

• items in chests, barrels, shulker boxes placed in the world, hoppers, item frames, armor stands or on the ground;
• items inside shulker boxes or bundles that are themselves in an inventory;
• players who aren't online.

Those keep their adjustability:dormant entry. That's harmless: it's inert data in a vanilla component. If you want them gone too, put the items in a player's inventory and flatten again, or edit them with /data or /item.

Removing a mod that adds enchantments

That's not uninstalling Adjustability, but it's close. If an enchantment from that mod or datapack was dormant on an item, Adjustability keeps it in the item's data, ignores it, and brings it back if you reinstall the mod (see When an enchantment is gone). If it was active, vanilla can't load the item and it's lost, with or without Adjustability; check the other mod's own advice before removing it.

Removing it from only one side

Adjustability is meant to be on both the server and the clients. A client without it may be refused by a server that has it, or join without any of its features; a server without it leaves clients' switching keys and panel with nothing to talk to. Remove it from both.