I hit send too soon on my other comment, but I did want to respond directly to this:

(I've mostly been searching here and the MobileRead forum, but I've also done Google searches and can't seem to turn up much.) Or I find similar threads that start like mine but have no useable responses. I'm not sure if I'm just doing a terrible job with search terms or if the information is just kind of buried, but I'm not finding a lot of relevant resources when I search. I just started looking into this possibility, but if someone has more information or can direct me to a good resource, I would appreciate it. I use Moon+ Pro as my reading app and I'm under the impression that it may be possible to get most of the CC functionality through Moon+ Pro. I'm not too concerned about the GUI as long as it's functional. I would also like the metadata to semi-automatically update when I connect my device to Calibre.

So with all that, does anyone have an actual alternative to CC that works similarly? I would like to be able to import the books to the app, show all the metadata (including a few custom columns), and sort/search through that metadata. It's frustrating, but the problems get worse as we get more updates to Calibre, it seems. However, I've been running into a ton of issues where it just will not connect or it'll disconnect while syncing with the library. I know Calibre Companion is pretty much dead in the water at this point - which sucks because I've been using it for years and have paid for it on three separate occasions (once for me in Google Play, once in the Amazon app store, and once for my grandmother's device) because I thought it was worth it.

Calibre companion app