I agree with your fact check but also want to point out that perhaps the original poster of this claim misinterpreted the article they linked with it. In essence, I found that the article linked directly opposes the claim, so maybe this is a case of misreading instead of deliberate misinformation-spreading. Even the link to the original posting in Bluesky is devoid of the claim that Colorado lawmakers are "loosening" school vaccine rules, which makes me wonder from where this claim originated. The linked article concludes that the bill which it discusses is supported by Democrats and opposed by Republicans, suggesting that the Colorado lawmakers are opposing RFK, a member of a Republican administration, and his policies, instead of following his recommendations. In any case, this claim is false, as you've determined.