I have a newborn, and my watch continues to tell me my sleep score is abysmal. That isn't likely to change anytime soon. I wish the sleep tracking was better, but I also kinda wish there was an option for personal circumstances that could acknowledge the "bad data" and have it not reflect on your health.
For example, I tracked my weight during pregnancy just out of convenience since I use the connect app for so much. The weight gain and slower training schedule did not reflect well on the advice the app was giving me. I know a normal person should be getting more steps in Garmin, but in the 3rd trimester, that isn't going to happen. I know I could have taken the watch off or not tracked these things, but then I wouldnt have an accurate picture when I return to working out.
Though that bad sleep and lack of exercise is definitely affecting your health very negatively, so the watch is just telling you the truth even if it is just a fact of life as a new parent you can't do much about.
On the open source side of things, I'll add that gadgetbridge is pretty rapidly making progress with Garmin devices. Might not be enough if you're deep into the Garmin ecosystem etc, but if you just want something simple and private, it's a good alternative.
I suggest using the nightly f-droid repo as there's new updates multiple times per week.
I ended up going with MFP anyway because it had the most matches to my local produce here in Europe (the competitors I was considering all mostly had US stuff). It's not perfect and the fact the food is user-submitted means you need to double check but it works good enough.
Anyway, from what I remember while there's only direct integration with MFP, I do believe you can get it to work by going through a third party app that serves as a bridge, like Google health, the apple equivalent or I think there's a few other non-FAANG options too.
I like my OG instinct well enough, but I also don't ask much of it. The Fenix 8 is pretty pricey though, pretty bullshit that they're neglecting the firmware.
I've had a handful of their watches in this line but this is the first time I was waiting for/excited about the new model and jumped at launch.
Like, out of the box no audio apps I use were available because apparently Garmin doesn't release the SDK unti launch day. Just crazy... Live and learn I guess.