In Shanghai - it's a mix of no detectors and very weird-looking body scanner type detectors that work at random times.
In Beijing the metal detectors at every station are there, but they're quite useless. Everyone alarms them with their phones, the security people wave the wand to make it seem like they're checking something and that's it.

Bags get scanned, but half the time nobody is watching the screen (though I guess there's some automated detection algorithms present).
More of a dog & pony show than real security, but it doesn't slow things down too much.
Also some stations have a temp scanner that you wave your hand over.

You might get a call from the Police to make sure you are who you say you are and to confirm that you have a negative test within 48h of arrival.

For now, IN Beijing itself - no restrictions of any kind.

This.

Flew back from SanYa to BeiJing last night. The NAT results were glanced at before going through security along with the green BeiJing HealthKit. Pretty smooth process.

Same process coming back from Shanghai. Test results went to the local health code app within four hours.

I remember there was an airport metal detector discussion in another thread (or maybe this one, can't recall) and I deliberately wore athletic shoes to ensure I had nothing on me in Hongqiao. Detector didn't go off, and I was waved through with no search.