I have 2 nest hub 2. Sleep sensing in the first one works well. On the second one which I just bought, after setting up the device I cannot find sleep sensing in the home assistant app so I cannot set up sleep sensing. Have reset it and it's still the same.
Thanks for visiting the Community.
Currently, you can only activate the sleep sensing feature using one account and device. If you want to use the sleep sensing feature on other device, you will need to use a different account.
Here's a link that will be helpful to you: Sleep Sensing on Nest Hub (2nd gen)