My understanding is that the "Temporarily limit 3rd party cookies" feature exists to test out the implication of a 1% 3P cookie phase-out that's enabled in Chrome currently.

This is the screen in question in Chrome developer tools:

From local testing, I am seeing that 3P cookie grants with this setting enabled are not respected and cookies for the 3P frame are still blocked despite the call to requestStorageAccess() not resulting in an error.