JFC. If you want to have Bluetooth on your #RPi (3B+) device you apparently 'need' to install the pi-bluetooth package, which requires the raspberrypi-sys-mods package which rewrites your /etc/apt/sources.list! Without asking.
If you want to do it without 'pi-bluetooth', https://github.com/raspberrypi/linux/issues/1314 has some clues.
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