Yes to all three: as stated in the specific page for Device Sync, nothing changes in the functionality (and Support) until the end of September 2025, i.e. for well over another year.
If you need to use Device Sync until then, please use the 12.x releases of the SDK, as the 20.x versions have that functionality removed.
If you’ve reason to believe there’s something not working in your app, feel free to open a Support case.