I’ve been using Zettle Notes with syncthing for a few years now. It syncs with my laptop as just a directory of markdown files that I also edit with Vim (plenty of good plugins like Vim wiki).

You may have a point about the obsolescence; my first VA4S got a stuck button about 10 months after purchase. That said, they did replace it with a new refurb for free when I reached out. Likewise, my wife’s apple watch battery is getting worse and is only about 1.5 years old and her only option is to buy the latest model or pay $$$ plus enough fees that it’s almost the same cost, (certainly not enough examples to generalize, but I’ve certainly formed my opinions from the experience).

I did this dance a while back and they all will use your data to some degree, so I opted to change the other side of the equation and maximized the utility as best I could and to do that I looked for a tracker that didn’t require a subscription for features that are already in the watch.

I opted for a Garmin watch, (a refurbished Vivoactive4S, specifically), specifically for that reason and also for long battery life (My wife recharges her Apple watch daily but my watch lasts all week and newer models last even longer).

If you are privacy-minded, you can obviously set up your Google connect account with a burner email, but much of the workout tracking does utilize GPS. You may be able to turn that off but I haven’t experimented there.