According to a news article about US MIL emails being accidentally sent to ML addresses due to misspellings, there was apparently a contractor in charge of the ML TLD, whose 10(?)-year contract was up the other day, I think, or will be soon. With Mali taking direct control over it, presumably they have their own ideas how to manage it. Why they wouldn’t or couldn’t have had the contractor do it (charge for domains) a long time ago, I have no idea. Doesn’t seem like something that would have to be postponed until the contract was over, but obviously I have no insight into the details of the matter.
I don’t use Calibre for this (but I do for epub and pdf ebooks). I use Plex and use Plexamp for my music collection. For audio books I used to have Chronicle Audiobook Player installed (which is open source, but not actively maintained) but am now trying out Listen Audiobook Player (which is not open source as a heads up). Both of those allow me to download books wherever I am.
If you have no interest in running a Plex server neither of them are suitable for you, but I just wanted to mention this solution in case you’re not dead set on using Calibre. Plex has a cost factor which may come into play (an obvious non starter for some). I have had Plex Pass for a long time so it was natural for me to use it, but might not be for you.