Mar 18, 2021: The flags #same-site-by-default-cookies and #cookies-without-same-site-must-be-secure have been removed from chrome://flags as of Chrome 91, as the behavior is now enabled by default. In Chrome 94, the command-line flag --disable-features=SameSiteByDefaultCookies,CookiesWithoutSameSiteMustBeSecure will be removed.
Although I'm quite happy for the new cookie behavior, I don't understand the reason behind removing those feature flag.
This kind of flags, as other feature flags like --disable-web-security or --allow-running-insecure-content, help developers to test a safe environment without browser extensions that often don't works fully as expected.
Now this feature is lost after the Chrome 94 update.