Docker-jitsi-meet does not use custom-interface.js as described

My docker-jitsi-meet instance (version -stable-7439-2) runs correctly, thankfully! I am trying the more advanced features with config.js (or to be more precise, custom-config.js)

Like others, I cannot get the ~/.jitsi-meet-cfg/web/custom-config.js contents to end up inside the running container’s /config/config.js file, the way Self-Hosting Guide - Docker | Jitsi Meet describes.

I of course have my volume in my docker-compose.yml because I have not touched that file. I have searched and search this forum and the Internet and have not come up with any steps to troubleshoot this yet. Please help me learn how to customize my self-hosted docker instance of Jitsi Meet!