There were .apt builds available up to CURA 3.1.0 - but evidently, that's where it stopped.
* https://www.techrepublic.com/article/why-i-have-a-problem-with-appimages-on-linux/
* https://www.reddit.com/r/linux4noobs/comments/kevz58/isnt_appimage_just_as_bad_as_an_exe/
But I guess CURA is open-sourced, so all that's really needed is for someone out in the community to build a version and throw it into a repository someplace.