I need some clarification on how iCloud works
So correct me if I'm wrong here, but when someone takes a picture on their iPhone, that picture is saved into the phone's internal flash storage by default, and if iCloud is enabled and synced, that photo is automatically backed up/copied onto it as well, right?
I thought it was as simple as that until I got the notification that my iCloud's storage was full and wouldn't be able to sync more photos (I've always had it enabled). A little while later, I log back into my phone to look at some pictures in the Photos app and see that more than half of them are missing. I checked the trash, and everything I was looking for was still missing. It wouldn't make sense to say that those pictures are missing just since they weren't synced with iCloud for some reason, because that would indicate that it wasn't actually backed up as a copy to iCloud from my internal drive; the file would've just gone straight to iCloud (not as a copy) instead of being saved on my internal drive.
The only reason I'm speculating this is because when I've tried to go back and few some photos in the past if my signal was bad and my wifi was down, the image would look like a low-res proxy to begin with before my phone took a second to download it to see in its original full resolution. But that of course got me thinking, "Wait, is this picture not actually stored in my phone's internal flash memory? Is the file only located in iCloud?"
Anyhow, immediately after I saw half my camera roll missing, I decided to just pay for iCloud+ to get the additional 50 GB storage. It didn't solve the problem, so whatever I'm not getting here is really throwing me off. All I really want is to get my photos back, but this whole iCloud conundrum shouldn't even be a conundrum to begin with. I always thought of it as an optional cloud storage system that you can use to backup all of your phone's data to, and although it technically still is, this is just adding a whole new layer to it.
What am I not getting here?
*iPhone SE 2nd Generation / iOS 16