Nice workaround! Thank you. It caused a paper conflict with CQRLog (Amateur Radio logging s/w that I use). The new lib works fine with CQRLog, but the package didn't know it, so I edited the .deb package for CQRLog, reinstalled it, and then I could use the libssl1.0-dev.
Really, Utilimaker should be including that library in the package as that's kinda the point of appimage: That it doesn't rely on external libraries. This is a product issue and should be fixed by their release / packaging engineers.