Seems its already in Arch's repositories, and seems to work, just add another flag to the invocation:

    yt-dlp --cookies-from-browser firefox --remote-components ejs:github -f "bestvideo[ext=mp4]+bestaudio[ext=m4a]/best[ext=mp4]/best" 'https://www.youtube.com/watch?v=XXX'

It is downloading a solver at runtime, took maybe half a second in total, downloads are starting way faster than before it seems to me.

    [youtube] [jsc:deno] Solving JS challenges using deno
    [youtube] [jsc:deno] Downloading challenge solver lib script from  https://github.com/yt-dlp/ejs/releases/download/0.3.1/yt.solver.lib.min.js

It would be great if we could download the solver manually with a separate command, before running the download command, as I'm probably not alone in running yt-dlp in a restricted environment, and being able to package it up together with the solver before runtime would let me avoid lessening the restrictions for that environment. Not a huge issue though, happy in general the start of downloads seems much faster now.