Worked at UPS from ‘03 - ‘05. I can tell by the labels and codes on the packages I get that not much has changed since then. Didn’t know anything about programming at the time, but I still spent plenty of shifts daydreaming about how the job could be automated or at least done by trained monkeys. 15 years later I can look back and pretty confidently say that it’s a much more difficult problem than I thought at the time.

Loading semis is basically 3D Tetris where you have to consider not only shape (boxes, tubes, cylinders, and everything in between) and size (fits in the palm of your hand up to 2- 3m long), but weight (basically 0-75 kg) and rigidity. Humans pretty easily develop and intuition for these things. I certainly unloaded plenty of semis that were for all intents packed to capacity. In theory you could probably have some kind of fully integrated system that let you know ahead of time the details of every package so you could model the entire load and figure out how to fit it... but doing what humans do loading on the fly would be damned hard.

Loading package cars (the brown delivery trucks) drops the need to maximize volume carried and adds constraints about the order and location of packages so the driver can find them. Again though, it’s a fairly loose system. In theory the load is pretty well distributed across the truck’s numbered shelves by the planning system... except all the days that it isn’t. A loader ends up making a lot of on the fly calls to overflow shelves and rearrange things so they fit on the truck and the driver has a reasonable chance to find them.

tl;dr - Anything is possible, but automating that part of the process is an enormous challenge IMO.