Integrated Switched-Capacitor Voltage Regulators will definitely be a thing in a few years they have already been produced in research labs and quite likely reached even limited production for low power <10W applications.
In general I agree with the GP look at how many unpopulated areas exist on modern boards.
How should you know if the lack of input filtering is because of poor design vs the fact that the spec of the power supply changed and you no longer need it?
If it’s not universally true and obvious it’s not a good test.
Modern boards are super complex I’m not an EE but I would more likely flag lacking probe points, probe points which are too far or too close apart or too far from common ground as bad design choices than try to figure out if there are enough caps for the voltage regulator without knowing the full specs of the damn thing.
For all i know that voltage regulator isn’t even being used anymore because the IC or PSU specs have changed mid production but because it was wave soldered with a different soldering method than the other SMTs they already had them on a bunch of boards...
If you can’t reverse engineer the board or the relevant within a few min it shouldn’t be in an interview.
Not an EE but I do a lot of HW RE if anyone puts a modern multi layer doubled sided board on my lap and tells me to point out what’s wrong with it in an interview I would ask them what’s wrong with them.