The opposite of modern is quaint. Modern means that it uses new technologies (Web/HTML5/React), quaint means that it uses old technologies (Win32 UI/HTML 4/command line)
You say this with authority. According to whom is web modern and everything else «quaint»? Not to be that guy again but electron-based apps feels nothing like modern, except maybe in the worst possible sense.
«Command line» is still very much alive as well by the way, and underpins a lot of things, say ci/cd.
Modern could mean technically not just stylistically. Like hackable in a contempirary language or use fancy tech like wayland. When we talk styles modern could mean anything, to some people it means minimalistic and functional, to some it means trendy