/usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf is in network-manager 1.10.6-2ubuntu1.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | [keyfile]
unmanaged-devices=*,except:type:wifi,except:type:wwan
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