theyycmonk Can be a paid blackbox or FOSS app.
I guess we are skipping self hosted solutions (?)
For the sake of completeness I would add that usb-c is always available for moving files, so you can rely on simple offline markdown editors (or even simple text editors).
The pros are:
- Completely offline (compatible with US requirement)
- Available in every OS: Android, Windows, Linux, BSD, possibly your TV, YouNameIt (Compatible with Linux availability)
Alas, this also comes with some downsides, like having to manually move your file(s) or setup a sync, plus less polished experience (lacking specific UI and features like mark as completed).
Going back on apps you could use, there are websites like disroot (This one seems to be based in Netherland, but maybe you want to double check) that already give you some tools to use.
At the very least, you can opt-in for a Nextcloud and synchronize your to-do list using caldav.
This solution seems to be US free and Linux compatible.
Disclaimer: I didn't check if disroot is actually trustable, it was just an example of service you can use that is located in EU.
I would also take a look if something in IzzyOnDroid is worth your time, probably starting from here.
In every case, whatever you choose, I suggest you to not rely only on https for your privacy and security.
If you can, enable e2ee so that also the server is not able to read the content of your data.
I think this will be beneficial independently on where your data is stored.
This way, if for some reason data leaks (Don't think only of data data sovereignty, keep in mind that also attacks or negligence are part of the equation) you have an extra layer of defence.
Note: CalDav doesn't implement e2ee by default