There is no one answer for this question. In my book IQ/OQ are for basic functions and operations and installation (needed to be tested once). PQ is for functions which may involve set-up procedures (like a filler, or an autoclave or a depyrogenation oven), or may have statistical control, and repeat runs.
PV should be done with heightened inspection of a full operating procedure (batch record, or master production record). But with a few additional inspection steps. But otherwise the PV really is to perform the operation as it would be done normally (same operators, same equipment, same procedures, same batch record).
For example, in a PQ, I wouldn’t mind the validation and engineers performing the testing. But in a PV, the day-to-day operators really should be doing everything (because that is what you expect normally and is your “process”.
So what requires a IQ/OQ/PQ: Sterilization always requires a PQ. Lines and/or trains should required a PQ.
What requires IQ/OQ: Simpler equipment should required IQ/OQ.
What requires IQ: Maybe an instrument, and the calibration certificate is attached. If it can be calibrated, then it should pass any OQ testing you might throw at it.
What about computer systems? Computer systems should require IQ/OQ (PQ should be reserved for capacity handling).
What requires process validation? Commercial processes, or aseptic clinical process where human trials are involved.
Then there is Verification. I reserve verification mainly for change controls to verify that there is no adverse impact. I might also do verification for a legacy process which may not have been properly “validated” formally, so testing is required, but the risk of compliance is very low (again because it is legacy with no reason to question the quality of the process).