P: When specifying a storage location on a different drive the application still uses the C:

This may be true for Lightroom CC classic, but I'm talking about the new "cloud" version, which doesn't have any LRCAT file. There is a folder tree full of stuff including "profiles", "TemporaryEdits" and "User" stored in %appdata%\local\adobe\lightroom CC\data, with no LRCAT file that can be moved.  There appear to be analogous files in a subfolder with a lengthy hex number name by the names of "Managed Catalog.xxx", but it doesn't appear in any way clear that these can be moved to another location and have the app recognize that fact.

Lightroom has a catalog file, previews and sometimes smart previews. These are stored by default in a folder inside your Pictures folder on the C drive. The 'storage location' you guys are talking about is probably the location of the imported images. That is something completely different, so you can have your catalog on the C drive and your images on the D drive.

You can store the catalog on the D drive as well if you want to, but you will have to do that manually. Here's how: Quit Lightroom. Open your Pictures folder and look for the Lightroom catalog folder. Copy that entire folder to the D drive. Open that folder on the D drive, locate the catalog file (it has the .lrcat extension) and double click it to launch Lightroom. Lightroom will now be using the catalog on the D drive. Just double check this in the Lightroom preferences, however. In the preferences you can say which catalog Lightroom should use; the most recent one (in which case all will be fine) or a specific one (in which case Lightroom may default back to the catalog on the C drive the next time it starts). Change this setting if necessary.

When all is well you can delete the catalog folder on the C drive.

I have this same issue. (The file path shown is bogus, although originals are being stored correctly in the new specified location (on D:\Adobe\...), but the C: drive location is still the one shown in the space available bar, and is still used for what appears to be catalog and other data.  It should really be possible to move all of the local files to a desired location rather than having them be forced to live on C:, which in my case is an SSD with somewhat limited space availability.