My understanding is that different devices measure HRV with different techniques, so they're not necessarily comparable. I've heard Apple Watch is especially bad at measuring HRV, while Garmin and Whoop are good.

One performance and health coach I follow recommends the Polar H10 chest strap to take a measurement every morning.

https://twitter.com/Alan_Couzens/status/1723334537235607989

https://twitter.com/Alan_Couzens/status/1473672665541984259

There's also not an absolute number or threshold that's good or bad. Generally higher is better, but what really matters are the fluctuations from a personalized baseline.