Love how Apple requires App Store free trials to last the full duration even if you cancel, but Apple's own free trials cancel instantly. Rules for thee but not for me...
I have not found this to be the case - just last week I signed up for a free 4 month trial of Apple Music and immediately (like, the next 30 seconds) canceled and retained my trial period. I have also done this with News and TV in the past.
That's great for you but I have TV+ and Arcade free trials and both end instantly if I cancel. And I'm not alone, lots of people across the internet experience this too. It's written in Apple's terms.