Post-COVID BKK turnaround:

Tried CX705-750, smooth as silk. All you need is to hold an (e)boarding pass for BKK-HKG.
For Green Code, ground staff will check it before you walk down to the boarding gate, and you will get a plastic note if you did not have a paper pass.
Then head to the gate, and the staff will print it for you.

Will also try CX751-CX708 next Sunday.