IIRC, HDDs have some reserved sectors in case some go bad. But in practice, once you start having faulty sectors it's usually a sign that the drive is dying and you should replace it ASAP.
I think if you know drive topology you can technically create partitions on platter level, but I don't really see a reason why you'd do it. If the drive is dying you need to resilver the entire drive's content to a new disk anyway.
You can pair your Garmin with GadgetBridge and it will all be offline and watch to phone only. I bought a Garmin watch, never logged into the official app and only use it with GadgetBridge without issue.
Download all existing literature to build a library for preservation and you're called a pirate. Download all existing literature from aforementioned library to train an LLM and you're a tech innovator. What a strange world we live in.
Sadly some parts of SFOS is closed source. I think it should work in the US, they just currently don't sell anything from their stores outside of the EU. Any community port should be able to run, but then without the official AndroidAppSupport and only with Waydroid.
Besides Waydroid there's also SailfishOS which has AndroidAppSupport, which works a lot better than Waydroid, but still isn't perfect. Of all the Linux mobile OSes, I think SailfishOS has the best design and ecosystem. You might have seen the preorder campaign for the new Jolla phone that might be interesting if you want to move away from Android phones.
Let Chatgpt read it for you