While testing 2020.4.28114 snapshot, I can't seem to find a way to count the items of a specific inventory slot of an entity when the GUI is closed. I found the procedure blocks for the "currently open GUI", like below...
...but I can't figure out a way to get the number from the inventory slot without an open GUI. I don't know if we should have a new procedure block like the one below?
With that it would be possible to decrement the number of items in the specific slot by the following approach:
I'm sorry if I'm just being blind and can't find the right procedure block... Maybe there's another solution too.