You will need to uninstall all updates to the YouTube app (disable and re-enable it in settings) and disable automatic updates for it in the Play Store before installing this module.
Just download the zip file and replace system/app/YouTube/YouTube.apk in the ZIP file (using 7zip or similar, I've also had success with MiXplorer) with your preferred YouTube APK, and install it in Magisk Manager. You probably need root to run this. Here are the replacements that I use, although you can use literally anything (OG YouTube, etc...):
Hope this helps somebody. To update, replace the APK in the ZIP file again, and install the new module. If you are running a full ROM under Magisk, this likely won't work and you should put YouTube in your ROM's ZIP file instead.