FontMixer is a GothLab extension that merges up to 100 fonts into a single file for use across Adobe apps. You drop or select TTF, OTF, WOFF and WOFF2 fonts, enter a name to generate an fmx_yourname.ttf file, then build, save and install it.
Once installed, the Text tab shows the fmx_ fonts, and editing the preview text updates styles live. You can create a new text layer with the selected font or inject an expression into an existing text layer, use a slider in the layer effects to change typefaces, or select a text layer in the app and click a font in the extension to apply it.
FontMixer uses unused font ranges, so its text is not readable as normal characters and the fmx_ fonts are not directly usable within other apps. Only numbers and Latin letters are supported. The limit is 100 fonts, and large packs can increase file size and may crash older Adobe versions.