Calibre doesn’t natively support reading DRMed files, but there are anti-DRM plugins which are trivial to install. You need to provide a legitimate Kindle serial number for Amazon DRM, as it uses that to de-encrypt the files. When you add the file(s) to your library, the plugin automatically runs as a file conversion. It basically converts it from a DRM-locked .epub/.azw3 to a DRM-free .epub/.azw3 instead. Since Calibre already has file conversions built in, the plugin simply uses that existing system to spit out a DRM-free version of the same file, then it adds that to your library instead.
This is the answer. It’s freely accessible, and duplicated across servers all over the world so it’s difficult for copyright claims to take down.