X11 XQuartz 1.20.11 (xorg-server 1.20.11) on Big Sur fonts not recognized

I have xset +fp the_directory with TTF fonts, I have mkfontdir and mkfontscale the same directory, I have fc-cache -fv and verified the directory is listed and cached and font count correct, but xlsfonts continues to not list the TTF fonts I want added. Fonts I want are included in in the files fonts.dir, fonts.scale and fonts.list. I've verified the fonts I want are in Font Book in User.

I think I'm missing something pretty obvious, but can't seem to find it. How can I get TTF fonts made available for use by X11?

So it turns out that xlsfonts does not list all fonts known, but rather either only the X server's fonts, or the fonts that are dealt with “classically”. fc-list will list the fonts that are dealt with in a more modern fashion (or that are on the X client?).

In the case of xterm, use the -fa flag to use TTF (and other non-bitmapped?) fonts. For example, if xset q shows directory X in the font path, and directory X has a fonts.dir file (made by running, e.g., mkfontdir X) and a fonts.scale file (made by running, e.g., mkfontscale X), and you've run fc-cache -v, you should be able to run (e.g.) fc-list someFontName and see all the styles that font contains, and be able to xterm -fa 'Input Mono:style=Regular', assuming Input Mono is a known font.