When will garmin add youtube music ?

It was not Garmin that did the announcement. Just rumors. 

So its not clear if it will come someday. 

At the same time as they add Apple Music. 

It's up to Google to make the app to work with their YouTube Music. No one else can do that. But since they got their own digital watch brand they are not so eager to help competition

You mean the disabled Fitbit type? xD My girlfriend has the Fitbit Sense 4... it's rubbish, I swear. No connections to Google to sync heart rate with other devices, no connections to trainers, speed sensors, no heart rate broadcast, nothing! Just a sleep analyzer xD Google will not make it any better because people on forums also see that it's a forgotten project for now.
PS. youtube music should be added by google developers nor garmin. garmin probably paid spotify to do that to have that on watches. 

You can put music from YouTube on your watch (I have over 400 on my 7x) but it's a bit of a fiddle, and nothing official.

You are pretty smart, it’s not „already available“, it is "now available“ since a couple of hours. This thread is from three month ago, when it wasn’t available.