What I expected to happen was:
The max stack size that can be visualised is the same with both inventory slots items and cursor items.

What actually happened was:
The max stack size that can be visualised inside of an inventory is 64, while it is uncapped for the cursor.

Steps to reproduce:

1. Join either a 1.20.2 or 1.20.3-rc1 world with operator permissions
2. Type: 

   /give @s minecraft:chest{BlockEntityTag:{Items:[{id:"minecraft:dirt",Count:127b}]}}

3. Place down the chest and open it
4. The dirt in slot one is displayed as having 64 items in it.
5. Pick up the dirt in slot one.
6. The dirt in the cursor slot is displayed as having 127 items in it.