App keeps giving me patronising advice on how how to improve muscular endurance even though it's a cardio activity I've been doing

Well, you did not tell what your question is, but let me assume you ask how to disable the tips. Since you did not specify what suggestions and where or when exactly you get them, personally I know about two possibilities:

1. Insights - you can opt out from the Insights in the Privacy Settings of your user profile. See the detailed instructions in Steps to Unsubscribe From Garmin Connect Insights | Garmin Customer Support
   
   
2. Daily Suggested Workout - you can disable the daily suggestions following the instructions in section "I Do Not Receive a Daily Suggested Workout on My Watch" of the document Using the Daily Suggested Workout Feature on a Garmin Watch | Garmin Customer Support, just (since you need to do the opposite), instead of enabling the prompt, disable it, in the last step.