Adobe has an FAQ on this: “The Pantone libraries that were part of earlier FrameMaker installations have been removed. If you have the latest version of Pantone color books and would like to leverage them for authoring, you can add them to the following directories - Adobe FrameMaker 2020\fminit\color & Adobe FrameMaker 2020\presets\colorbooks.”
If you want instead to just specify the color, getting the Spot name to survive into the .ps or .pdf output, so it will be visible to pre-flight, might require an extra hack. See this old thread: PDF files with wrong colors
If you do define your own name, let me disagree with Klaus, and suggest that you do use the Pantone library name that your print shop will be expecting to see, and to have enterprise naming/color_catalog consistency. Just don't sell or publish a list of such names.
But what might be really required is to review the color intent for the document. If screen viewing and convenience printing is the goal, it might make more sense to use sRGB (for which Pantone specs exist). As FM has no color management, you need to use PDF workflow tools to tag objects for color management [sRGB IEC61966-2.1]. If this includes text colors, there can be a further problem with final file size.