I installed the new beta and tried to install HIIT Workouts, its not possible because GCM thinks the FR945 is incompatible.
Checked on Android with the same result. 954 listed as incompatible. Also checked that my GCM is upto date.
I assume you've already raised it with the beta team?
Tucked away somewhere in this thread - https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/275791/fenix-6-series---19-74-public-beta
are similar comments, I think with a response from Garmin.
I just downloaded few HIIT workouts using android GCM. After adding have you pushed them to the watch?
This is what I See on Android
Solved: They changed something in the Backend, it is working right now on iOS (no App Uodate needed)
and yes, I reported it via eMail, but only have MacOS and iOS devices at hand so I wanted to also get it out here.