There is an interesting response from John Mueller of Google on what to do with URLs that may appear duplicated because of URL parameters, like UTMs, at the end of the URLs. John said definitely don’t 404 those URLs, which I think no one would argue with. But he also said you can use the rel=canonical because that was what it was made for. The kicker is he said it probably doesn’t matter either way for SEO.
John Mueller Of Google On 404ing or Using Rel Canonical On URL Parameters
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