You can launch Chrome using the --test-third-party-cookie-phaseout command-line flag or from Chrome 118, enable chrome://flags/#test-third-party-cookie-phaseout. This will set Chrome to block third-party cookies and ensure that new functionality and mitigations are active in order to best simulate the state after the phase out.
You can also try browsing with third-party cookies blocked via chrome://settings/cookies, but be aware that the flag ensures the new and updated functionality is also enabled. Blocking third-party cookies is a good approach to detect issues, but not necessarily validate you have fixed them.
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