How do you make the netherite chest upgrade? I am using fabric 1.20.1.

They don't seem craftable yet, but this mod has almost no documentation so I just checked JEI and tried in creative mode (no result).
For myself, I'll be adding custom recipes for it using CraftTweaker cause I want to use it already.

You can craft them, instead of the Smithing Template used to upgrade Diamond Gear into Netherite Gear, you place the Diamond Chest/Barrel/Upgrade there. Then just add a Netherite Ingot and the upgrade should work. I believe JEI fails to show this as it isn't the normal way to go from Diamond to Netherite.

Edit: I did fix this for my modpack. I changed the Recipe so that the normal Smithing Template goes where it should, then you put the Diamond Chest/Barrel/Upgrade where you would normally place anything Diamond that you want to upgrade. Finally, you add the Netherite Ingot and you're good to go. This also works with JEI as it now shows the Recipes.