Totally normal. But at the same time he should clean up his spills

We use a placemats that has a space for cup (and plate and utensils etc). It makes such a difference for our 1 and 4 year old. Coaster would also work, but could cause issue with unevenness depending on size. They spill all the time when the placemats are in the dishwasher. But pretty much never spill when they have their placemats and that visual reminder of where everything goes.

Use a cup with a lid until he gets better

Coaster helped with this in my house. Visual reminder to put it where it wouldn't be knocked over.

Could be a growth spurt causing awkwardness.

YES!!!!!!!!!!!!

Remind him not to leave it near his elbow. That's how milk/water gets spilled in my house. Have a dish towel handy for him to clean it up.

Somewhat typical based on how long he’s been drinking from an open cup.

Do you notice any other depth perception issues?

Yup...completely normal

DS turns 5 in a few days. It seems like at least every other day he knocks over his water or milk glass. It happens at home, at other people’s houses with their cups, etc. Is this typical?