could you add a tier 4 ? with maybe the recipe with netherite scrab or netherite ingot

Sorry, but adding more slots is not possible. Tier 3 double chest screens barely fit on the screen with normal GUI scale. If I would add more slots, there would be people that complain about the inventory not fitting on their screen.

you could add vertical slots similar to iron chest mod

Can you show me an example?

all gui of iron chest mod is vertical direction....

I have no clue what you mean with that

You are using another GUI scale. This isn't working with people that use a higher GUI scaling.
What I sent you is the default GUI scale.

the first 3 images are with gui scale 3 and the last 3 images are the default ones

you have developed all the gui of your mod horizontally... you could to enlarge the gui develop the gui vertically

There is no space as I already said.

I already use 512x512 textures instead of 256x256, but adding more vertical rows wouldn't fit some screens.