I have used an app called Happy Scale for a 7 day smoothed average (other options too) for about a decade now. 4.9 stars. Tag line, Conquer Scale Anxiety! https://apps.apple.com/us/app/happy-scale/id532430574

It’s developer, Russ has struggled with his weight, and he is always improving the functions. free version has predictions based on hitting milestones to goals, but long term forecasting and other upgrades are in the paid version, which is reasonably priced. It syncs with Apple Health, your scales, or enter your daily weights manually. Easy to use, free version enough for me.

There is a Trend function built into Apple Health for weight, but I haven’t used it. I have a Renpho Bioimpedance scale that automatically syncs with Apple Health..that's enough of my data for Apple to grab