I was using speed-up in 10.14... It doesn't work anymore in 10.15
And that speed ajustement is very usefull for my use (transcription)
Big thanks !
Welcome to the forum.
It sounds as though the problem is not one of controlling a playback application (which KM might be of help with) but of your not currently having a suitable application with the demise of Speed-Up. So I think you will need to find an alternative. Many audio editors (e.g. Audacity) provide a way to change the speed of playback, but if you especially want integration with Apple Music/iTunes, I don't know what is available.