I learned all this the hard way after buying a bunch of now useless PH-2.0 4 pin cables.

What do you mean by Useless PH-2.0 4 Pins?

Grove cables are fully compatible with M5Stack products and HY connectors are compatible with PH as long as they are 2.0 pin spacings.
the only difference is that some are flat topped, some have locating fins and some have clips. I have a selection of various types and have even modded several including posting a guide and a comparison on the forum of the difference.

There was some confusion at one point with the White and yellow wires reversed but that has been solved and its not hard to swap the pins in the housing as again I have made a guide on it.

The physical label on the ATOM incorrectly describes the connector as a PH 2.0-4P. The product description, under the "Specification" section calls it a GROVE connector.

The technically correct description is an DL20005 (HY Series) 4pin connector. Near as I can find the original manufacturer is DLL. Full specs are here.

seeedstudio adopted this connector and integrated it into their product line, giving it the GROVE trade name.

So, if you're looking for cables, look for ones marked with GROVE 4 pin or HY 2.0 4pin (female) connectors. Searching the web for HY series cables will produce a few hits, or they can be sourced through seedstudios or M5Stack.

When buying, you'll find "buckled" and "unbuckled" versions. "Buckle" refers to cable connectors either with ("buckled") or without ("unbuckled") a captivating latch. For the the ATOM, both work. For other boards the latch may interfere with their packaging, so you'll need the unbuckled version.

Also note that if you're buying cables with connectors on both ends, you might find "standard" and "reversed" pinouts. You'll most likely want the "standard" type, which means pin 1 is connected to pin 1, etc., instead of pin 1 connected to pin 4 ("reversed"). "Standard" is the seeedstudios standard.

I learned all this the hard way after buying a bunch of now useless PH-2.0 4 pin cables.

M5Stack folk, if you monitor the forums, please change the label on the ATOM to say either GROVE or HY 2.0 4P. Please 😄.

(Edit: Just noted that the M5StickC PLUS does correctly label this connector as HY2.0-4P. So some M5Stack folk are aware of the difference.)