Try changing "run" to "do".
Make sure there are no other languages in google home/assistant ap except english only.
Try making a "workout" task and see if google assistant will run that routine.
Try going into google home routines and make a routine called "workout" which does the custom command "Do fred in tasker".
If you play around with those things, you might get something to work.
The other thing you could do is use IFTTT with Google assistant.. to send a text to your phone and have tasker get the text then run the task.
I've had that same problem.. as well as many others. Google's algorithm is messed up and sometimes it wants to do a search instead of the task. Some words work well with launching, others don't. LIke my "couch finder" task it wants to do a websearch.. but workout command seems to be recognized and runs tasks.