Just a thought about Garmin. In theory it sounds great. Yes, you can disable all account/cloud upload and syncing. Yes, you can take data physically from the device itself and yes, you don’t need the account. But you have some basic telemetry only. If you’re using it just for running and a step count it’s probably fine I guess. But for anything else you’re forced to use the cloud anyway.
I tried btw, but it’s so big pain in the ass that I gave up. You have to think about it, because the device has a limited memory for just a few days, you have to find a tool that you can use to process the data. I tried several and it never worked well. Only one kind a good was https://intervals.icu/, but it’s again online service.
Anyway I gave up. Created new email alias with a fake name, put some BS data in and block (hopefully enough) the tracking from the app.