Kindle integration using myclippings.txt instead?

Despite exhaustive searching, I have no options to export my Kindle highlights via email from any platform (e.g. Kindle Paperwhite, iOS app, Mac app, web). I think that may be because most of my items are sideloaded (aka not from the Kindle stores), but it's hard to know 100% when my only evidence is an absence.

In my previous PKM system (shoehorning Diigo), I was able to add my Kindle notes by uploading the myclippings.txt file. Is that an option in Capacities? If not, might it become one?

My motivation: Readwise is prohibitively expensive, and I'm desperate to leave Diigo -- they've broken their Export option and aren't responding to support requests, even from paid users (which I've been for 15 years). They've been going downhill for awhile but it's critical now. Capacities has the visual/block management of wiki features that I crave, but I need a home for Kindle notes.