For Chrome:

chrome://flags/#same-site-by-default-cookies

chrome://flags/#cookies-without-same-site-must-be-secure

I found that at least the #same-site-by-default-cookies flag behaved as I would expect when setting it to "Disabled". Use case was to load an iframe that sets it's own cookies with no SameSite value and still have that value default to "None".

We fixed this issue properly ("SameSite=None; Secure" in the cookie set in the iframe), but using the #same-site-by-default-cookies flag was a workaround for a little while.

What was a bit strange was the default behavior on Chrome was different for users even on the same Chrome version. They seemed to be rolling it out in phases. More info on that here: https://www.chromium.org/updates/same-site