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.
They are right that Garmin sleep tracking is pretty inaccurate though. Not so much the length, but identifying the sleep stages correctly. But yeah, it's like how drinking alcohol fucks your HRV up, it's just showing the issues alcohol can cause.