In Singapore Changi, the arrival and departure are at same gate so you can just sit and wait for next flight. Passport is checked before you get into next flight at the gate where they check your boarding pass as well..right there your bags are also scanned (at each gate or group of few gates)

Just transited in HKG, the gates are same but boarding at different levels. So you clear the security at a common area, get same PP checks done then go to departure gate which is one level above. IIRC Qatar etc are the same.

But PP checks do happen in both cases.

Big difference between airline employee checking whether or not you're the ticket holder and the government checking every passenger for warrants.

The false positive rate when doing this via passenger records alone is so high that airport law enforcement will generally only go out of their way to actively look for particularly interesting people.