This has got to be the simplest point of attack to handing the graphical side to an inventory , in a lot of cases things like the scrollable lists are used with widgets that themselves are lists just in a different orientation , this works but is just more complex so why do this to yourself in this modern era of UE5.1+
( why is the thumbnail offset to the left )
Setup the inventory item widget , in the top righthand part of the screen set the size of the widget to custom and make a size
Drag in a canvas and a Button
un believably thats it and all you have to do just for starters , you can style the entry from here but this gives you the base thing