Get a smartwatch with Gadgetbridge support and keep your data on your phone.

There's also FitoTrack which is an open source, local android app for fitness tracking

https://codeberg.org/jannis/FitoTrack

HealthyPi Move is open source (including hardware) and doesn't send data anywhere (only locally to the app being developed). It's available for pre-order at this time.

Garmin then use the FOSS Garmin connect app I forget the name. You get all the fancy important data and monitoring. None of the worries. Or just don't sync your data and monitor over time on the watch itself. Batteries are second to none. Garmin is the way to go. I've tried them all.

Gadgetbridge?

Pinetime

What are you looking to track? Also, don't worry if you don't know how to self host, that's what the community is for 🙂

Pencil and paper. In a small safe. :(

Do you have a URL to this foss app?

You could try Withings. I believe they're based out of France.

Not sure, but maybe a Casio G-Shock? You'll likely still be spied on, but maybe not by the US? Personally, i wear a Huawei,,, oh well.