Linux has been effectively Unix™ for me ever since the days when Dennis Ritchie indicated that he used Linux for everything on his web page. Late 2000s at the latest, maybe early 2000s. Unix enough for Dennis should be Unix enough for anyone.
I've been using Linux for 30+ years now and have always considered it free (as in speech) Unix. For my purposes, the difference was always more legal and philosophical than practical. Of course, I was a student back then and didn't need to run the commercial software of the time.
Caring about which systems are branded UNIX is like caring about which NBA player was paid to endorse a particular brand of athletic footwear.
Well he and others moved away from UNIX, created Plan 9 and Inferno.
In these efforts they also tried to create successor languages to C, Alef and Limbo (for userspace), and never cared that much about anything past C89.
He has settled with Linux because that is the winner of UNIX wars, which predated Linux wars on Distrowatch.
As for the original UNIX,
"Using Unix is the computing equivalent of listening only to music by David Cassidy"
-- Rob Pike