Incorrect sleep track data on Apple Watch SE and iPhone 12 Pro Max

I've been using my Watch (series 7) and iPhone (12 Pro Max) to track my sleep, but the data I can check is not accurate. Last night I was up (as in, walking around) between 4 and 5 am, and I then struggled to get back to sleep for at least an hour, but the app marked the whole period as REM sleep. Are there better DIY sleep tracking options out there? Especially for apnea? I'm close to giving up on this watch (it just went through a phase of jumping 4 hours ahead when out of Bluetooth range of the phone, but that's another story).

[Re-Titled by Moderator]