There's a paper referenced here - https://is.engin.umich.edu/stories/tool-to-analyze-the-security-privacy-of-vpns-wins-first-place-for-applied-security-research-in-2022

And the group only found 3 VPNs that are even close to what they say they are: https://www.consumerreports.org/vpn-services/vpn-testing-poor-privacy-security-hyperbolic-claims-a1103787639/