Just a warning. It may be displayed clearly somewhere but I missed it.
When I find I’m not getting enough out of an app subscription I’m using, I usually go into my account ahead of the expiration date and cancel. The subscription or trial keeps running until the planned expiration date and ends then.
So, I did the same for the Apple TV+ trial I got nearly a year ago with my new iMac, but it cancelled immediately, even though the UI for cancelling is the same one as for app subscriptions.
When I am subscribing to “new” stuff via the AppStore, I tend to cancel the subscription immediately. Just to be safe, if I forget doing so later.
When I was going to do the same for my “free” Apple TV+ trial, there were warnings in the UI that prompted me to be aware of the fact that this cancellation would have an immediate effect. So, I did not go through with the cancellation and I created a reminder to cancel the subscription later.
End of the story: I ended up subscribing to Apple One later on.
I even end (some) subscriptions on the day I start them, but not the free Apple TV+ trial, because in my case Apple clearly mentioned that it would end immediately.
The cancellation UI is the same but the immediate cancellation is nevertheless mentioned explicitly. But it’s good to have a reminder for people who may not notice. 
Could this depend on where you do it? I did it via the app store on my iphone and don’t remember any particular warnings.
No big loss anyway, I had less than a week left and wasn’t watching much.
Also got a trial when I bough an iPad a few months ago but that didn’t seem to add to the available time, the end date stuck to the initial trial one.
I did it via the app store on my iphone and don’t remember any particular warnings.
That’s where I saw there was a catch to cancelling early. 
I guess it’s the app store equivalent to banner blindness for me then 
FYI, the same applies if you activate a trial from Apple Arcade. I also saw the same warning on my “complementary” first month of Amazon Prime.
It is almost as they are hoping that we forget to cancel on the last day so they can bill us for another month, right? Nah, that would be too cynical for the richest corporations on the planet…
You get reminder emails for all subscriptions due to be renewed or expiring. In that case, you can’t blame Apple for not overextending the free trials, and they don’t try to con you into forgetting. I’m all for criticizing Apple when it’s indeed deserved, but let’s try to avoid bad faith here.
It’s still kind of strange to have a different behaviour from a UI that usually acts pretty consistently so you stop looking in detail.
Is it deliberate? Probably not, there are other strange patterns in the App Store. My “favourite” being displaying the text “processing payment” when I download a free app. My heart missed a beat a few times on that one.
The sign up process for these free trials is nothing like anything else in the store (you have to activate them in specific sections). Anyway, when I’m offered something, I’m always extra careful to the fine print
IMO, everything Apple does is deliberate.
You will receive an email regarding an AppleTV+ free trial expiring. I got mine 5 days before and another a day after. Had to maximize my trial before I decided to sign up for an Apple One bundle.