Or at least Echo/Nest in the UK?

You're not missing anything. Tidal didn’t stream smoothly to my Echo devices, and there was no personal playlist support through Alexa.

A full 73% of the Alexa skill for Tidal ratings are one star.

I know you're in US, definitely using a Amazon US account? Haven't recently moved there and using non-US account?:)

https://www.amazon.com/TIDAL-Music-AS/dp/B07KK5VKD2 is skill enabled?

"Alexa, play Mymix1 from Tidal"

Also, if you look at the Tidal skill reviews on Amazon.com , they’re not great

https://www.amazon.com/TIDAL-Music-AS/dp/B07KK5VKD2

It's actually a skill: https://skills-store.amazon.com/deeplink/dp/B07KK5VKD2?deviceType=app&share&refSuffix=ss_copy