Stacking and sorting as a concern? Those are things every toddler should be doing. There are a billion toys designed precisely to encourage kids to understand how sort and group by color, shape, you name it, or to repeat patterns, etc. And little kids are often serious about their tasks, whether it's stringing beads or building a fort. Little kids are also often weird. Atlas doesn't even seem particularly weird, tbh, much less worryingly enslaved to systems or devoid of normal emotional range.
Yes, "no one can know for sure," but the reality is that it is far less likely to be present than not. The default, the norm, is not autism nor a million other conditions that most people do not have. So odd to keep coming back trying to jam the kid into a developmental delay or concern. Every personality tic or being quiet or self-contained doesn't equal a "condition." Pretty sure Robyn has said he & Glenn are quieter, introverted types (?), they don't seem to have a big social circle, and Atlas isn't around other kids much; makes sense he might be a more interior type as well, at least for now/ when patterning off of what he sees day-to-day.
What is the reason for even putting autism out there as a thing to look for, other than the fact that it's the diagnosis du jour, and every last quiet or quirky person thinks they (and everyone else) have it?
