Linear DNG is a standard DNG and was always supported by Lightroom, I've used DXO for several years and that's how I got embedded profiles in the first place. Apparently current Lightroom also supports them, but somehow forgets at some point. If that's the case it's a bug.
Camera matching profiles are irrelevant, they are just everything defined by Nikon, it's always the same set.
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I see the same behavior with sample dpreview.com mosaic DNGs taken from the Hasselblad L20D-20c, which contain embedded profiles.
When you switched the profile from Embedded to Adobe Standard and then browsed the list of profiles, you didn't see Embedded because it is in the Legacy profile group, which is hidden by default. To unhide it, right-click the profile group Adobe Raw and do Manage Profiles; then check Legacy. The Embedded profile will now be visible:

(This would have been a lot easier to diagnose if you had provided a sample DNG.)