Your friends anecdata is entirely irrelevant until they've separated and we hear about how that plays out, before it's even remotely worth hearing as still meaningless anecdata.
Even in those seven, it's not something that happens automatically. For example, in Utah, it only applies to those "who hold themselves out as and have acquired a uniform and general reputation as husband and wife."[1]
If my meaningless anecdata isn't remotely worth hearing about, then what's to be said about your intentionally misleading irrelevant statement?
*Oops:
[0] https://www.ncsl.org/human-services/common-law-marriage-by-s...
[1] https://le.utah.gov/xcode/Title30/Chapter1/30-1-S4.5.html?v=...
It generally does not require a ceremony (but it does usually require an explicit mutual agreement), and living together does matter (cohabitation is commonly a requirement or evidence of common law marriage), but other than that you are right that publicly presenting as married is often a requirement (and otherwise is evidence).
Here’s info from Texas as an example, which is more required-elements-based and includes cohabitation: https://guides.sll.texas.gov/common-law-marriage#:~:text=Tex...
And here is Colorado, which is more evidence based and does not identify cohabitation as even a form of evidence (though it does have joint ownership of property): https://pitkincounty.com/288/Common-Law-Marriage
Utah is more specific requirements, and includes both cohabitation and how the couple presents publicly, but no ceremony: https://www.utcourts.gov/en/self-help/case-categories/family...