Where to Find Condo Rentals

Curious why you feel the need to go outside Streeteasy?

The REBNY listing system (RLS) is still up and running. I would think you could access it through NYT.com, though I haven't tried lately.

There are certainly other platforms, but I can't think of any one which could be described as "one main platform" OVER StreatEasy. For example there are those which publish the entire REBNY feed instead of just those that pay the daily fee to post rental listings (which StreatEasy has slashed but I don't think eliminated https://therealdeal.com/2020/03/19/streeteasy-slashes-fee-to-post-rental-listings/ ) but those same platforms don't have the same direct from owner listings which are absent from the REBNY feed.
There are also sales listings which agents are chosing not to place on StreetEasy as well as FSBO which are on StreatEasy but not showing up on REBNY feed.

As far as Sponsor listings go, the vast majority don't show up anywhere because they are allowed to "hold back" listings and not release them even if they are on the market as far as being fully filed Public Offerings go.