https://youtu.be/1menRgbal-Y very rough example with download,
also search the forum for user Flakky who had a thread here somewhere.
He has a Russian channel with a downloadable survival game with a rough example.
https://youtu.be/1Ny2gwR_rSk if you can speak Russian… this may be all you need?
the main bit to look at is the check distances to edges and checking columns and rows for empty slots, the order of “for-loops and loops” and understanding the logic.
Both of the above are rough with limits functionality,
but for free they are fantastic and those guys awesome,
useful as a starting point to get the basic idea, you will still need to put in many hours to make them usable.
The multi slot inventory’s on the market place are very reasonably priced, even as a learning resource and maybe your best bet on a usable example.
Haven’t really looked so not sure if these are exposed blueprints you can examine or plugins??
There is also another thread here somewhere, think “Diablo style inventory” could be the search term to use, that thread has a run down of the basic principles.
Hope this helps…