The problems with the newest GoPro cameras overheating is when they record 4K/60fps or 5K/30fps for over 30 minutes, in general warm conditions or warm areas.I question how much experience you have with Go-pros. The problem is, they overheat. If you subscribe to any major YouTube channels, most of them do use GoPro cameras, but it’s one of the biggest gripes discussed is that they overheat, which either causes a temporary shut down or even memory loss. For me, for an iPhone as an ‘action camera’, I’ve never had that happen, ever. So in that respect, the iPhone trumps GoPro without contest.
I have the GoPro Hero 9 Black. I’m also an iPhone 12 Pro Max user.
As an action camera, the iPhone can’t compare. Due to the dimensions and durability of the GoPro you can place, mount or position the GoPro in places you wouldn’t even dream of doing the same with your iPhone. There’s a reason action cams like GoPro’s exist.
Back to the GoPro overheating. As I said, this is when recording over 30 minutes of video at 4K/60. The most intensive video recording, in warm conditions. On a handlebar mount of a bike (which is the point of the Apple warning), this shouldn’t be a problem as there will be plenty of cooling to the GoPro body during movement.