should I suspend a floor-standing turntable?

The floors of a high-rise building are often worse than the suspended timber floors of a house for Structure-Borne feedback (and that's the only feedback that you need to worry about)...😫
Your safest bet is as close as possible to a structural column or the core containing the fire stairs and lifts if that is possible.
Being in Southern California.....the building will have been designed for earthquake loading with flexible steel columns and beams and probably prestressed concrete floors....😱
Good for staying alive....but the worst recipe for audio happiness unfortunately....😢
Good luck....🏢

You could hang it from the ceiling with monofilament, etc. I heard one like this and this method is very effective

Wood blocks can be found at lumber stores cheap and granite slabs can be found in monument shops -- work out the best price there. You don't need one size of monument for sure :-)

After you select one of the above options, if there is still any uncertainty whether you have overcome all manner of vibrations, there is one more inexpensive step that I have found to complete the job.
Try positioning three or four Cryo'ed hardened steel compression springs named "Cryo Baby Promethean Mini Isolators" (from Machina Dynamica) between the turntable bottom and the support surface of wood or granite. And/or try a set beneath the wood or granite, itself.
You are now better protected, and may proceed to engage in safe sound.
Listening to some favorite recordings will tell you whether each step you take toward better isolation is actually delivering more natural and satisfying audio in your system.

..just remembered....another excellent way to support the turntable is to attach the stand to the wall using turnbuckles (at Home Depot). Tighten the rig and you'll be amazed at how much better things sound.