During idle time, the watch automatically registers as daytime nap (fake)

Welcome to the club!

Garmin is tracking inputs on this thread

https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-7-series/325065/night-sleep-data-gets-replaced-by-daytime-sleep

Make sure you post and contact Garmin-Chris there to add your case to the list

Oh, and the only workarounds are the following options:

- disable the WHR outside of activities, or always if you have a strap

- disable the WHR in the battery saver mode, and put the watch in battery saver mode. The WHR will come back during an activity, but you will have to re-enable the battery saver mode manually afterwards.

- not wear the watch outside of activities and sleep (this is what I do now)

The downside of all these options is that your fitness tracking features (like steps, floors, move IQ events) won't show. You will also lack stress measurement which will take your training readiness modestly down (but it still can get in the 80 range).

I have not had a sleep overwrite since I updated to 11.28 and I have not changed my habits since then. Previously I had sleep recorded when I dosed off whilst watching TV for periods up to around 2 hours, but only the actual sleep periods were recorded and not the immobile phases before or after I fell asleep.