How to isolate turntable from footstep shake or vibration

Sorbothane Feet

Read this article from Stereophile back in 1995
https://www.stereophile.com/reference/52/index.html

Your turntable has springs so first check that the suspension is correctly set. Otherwise i would go with a dedicated stand or a wall mount solution.

That is disappointing. It means that vibration is getting to the sub chassis in spite of the suspension either through a poorly designed suspension or directly vibrating the sub chassis. You can try damping the suspension by stuffing some foam in the springs. Later versions of the Oracle add adjustable damping. Subwoofers are a huge problem for turntables especially if you have them set where they should be. The low frequencies will fibrate the tonearm directly through the air. It is very important to use a subsonic filter and digital filtering is the only way you can do this effectively without injuring the bass. I roll off at 18 Hz 80 dB/oct. I use a Sota and a large subwoofer array and have absolutely no issues. The turntable is however on a very heavy cabinet on a concrete sub floor. I have used the Sota on several wood floors over the years without any difficulty and have seen SME's and Basis tables do the same.  Adding mass under the table usually does not help. The floor just bounces at a different frequency. There is a chance that the problem is not vertical vibration but lateral vibration in which case using a sturdier rack and damping the springs will help. You still should look into a subsonic filter.

I do not use a suspended turntable but I have had successful isolation using an HRS platform (S level) and a Vibraplane. They both work well independently and even better together.  Obviously, I would try some simple footers first as you could end up spending more on isolation than on the turntable itself.