This page is a static copy of the demo. It used to run on Apache, set a cookie named TestCookie and add SameSite=None; Secure to it for browsers that the rule below did not exclude. This copy runs on BusyBox, so it sets no cookie and does not check the user agent.
The demo showed that Safari 12 and Chrome 79 treated the same cookie differently. The Apache rule that worked around the Safari bug was:
<If "%{HTTP_USER_AGENT} !~ /(iPhone; CPU iPhone OS 1[0-2]|iPad; CPU OS 1[0-2]|iPod touch; CPU iPhone OS 1[0-2]|Macintosh; Intel Mac OS X.*Version\x2F1[0-2].*Safari)/i">
Header edit Set-Cookie ^(.*)$ $1;SameSite=None;Secure
</If>
Place the rule in an .htaccess, httpd.conf or virtual host file to try it on an Apache server. The regex is outdated; see the WebKit bug for current guidance.