I’m not sure this is correct. Apparently Chrome will start blocking cross-site cookies at some point.
“Cookies for cross-site usage must specify SameSite=None; Secure to enable inclusion in third party context.”
I’m including the Hubspot tracking code in my company website that is not powered by Hubspot. That tracking code sets a cookie that doesn’t include a SameSite attribute. Some browsers will apply a SameSite=Lax in that case. If that cookie as also a cross-site cookie, which this is, it is only a matter of time before browsers block that cookie. My reading is that only if you set SameSite=None and the Secure flag will the browser allow it to be set.
SameSite cookies explained | Articles | web.dev - Some browsers have a bug where setting SameSite=None is treated as setting it to Strict. So some feature detection would be required. Also setting the Secure flag would require all users of your tracking code to be using https, not a bad requirement, but may break some customers tracking.