In a discovery made by Redditor u/stephenvsawyer, it seems that there is a loophole which gives iPhone users free unlimited original quality photo storage on Google Photos. According to the post, it seems that this seems to stem from how Apple shoots photos on the iPhone, where it uses the HEIC format and not JPG.
“With all modern iPhones shooting photos in HEIC format, which is smaller than even Googles compressed JPG files, iPhones therefore get free unlimited ORIGINAL quality backups simply because it would cost Google both storage space (because if Google tried to compress iPhones HEIC photos they would actually become larger) and computing power (because Google doesn’t need to compress and process all of the billions of photos iPhones backup.)”
However, it should be noted that while photos can be stored in their original size, videos will still be downgraded to 1080p.