I had wrapped up the last post about this (YouTube Music Scrobbling on iOS) suggesting FoxxMD/multi-scrobbler. While this is a great tool, with YouTube Music specifically it had a few issues due to how the YTM API works. If you are interested, you can read the issues, #156 and #158. The first being songs are sometimes scrobbled multiple times to Last.fm, the second issue being YTM invalidating the token every 30 minutes or so.
So now what?
The Solution
I ended up commissioning my friend Mario to make a tweak for the iOS app that can be loaded with side-loading or via a jailbreak.
https://github.com/marioparaschiv/lastfm-yt-music
However, I also have my fork of it that adds a dockerfile to build it, which will net consistent results regardless of your system’s configuration, and without the need to download any SDKs.
https://github.com/someaspy/lastfm-yt-music
In both cases, it is quite easy to do. I’ve written the readme file for both to be easy to follow, so I will skip detailing it and just suggest you follow the readme on the repository.
Additionally, since this is only a tweak you need the original .ipa file to inject it into. While there are several websites that host .ipa files for various apps, I host YTM .ipa files I pull from my jailbroken iPhone 8 at ipa.aspy.dev/youtube_music/stable/ (Dead 2/26/26)
You can also pull your own using Frida, but I believe a jailbroken device is required to extract .ipa files.