- For wallpaper engine you could check out wallpaper engine for kde. That will allow you to select wallpapers directly from your wallpaper engine library.
Not sure if that is what you mean, but you can also add different “redirection targets” for different addresses on the same domain in the free tier.
https://improvmx.com/ may be what you want.
I have been using ultra.cc for over a year now and so far it has been pretty great.
Do you already known about https://doc.qt.io/qt-6/qtbluetooth-index.html? That should give you cross-platform Bluetooth access with a single API.