I have a subscription to the 50GB iCloud Photos. It contains 50GB of my photos. I hope to back up these photos to my Windows laptop. I've downloaded iCloud for Windows and synced the photos from iCloud Photos to my Windows laptop. However, I notice a big discrepancy between the total size of the photos I downloaded and the total size of the photos on iCloud (32GB on my Windows laptop vs 50GB on iCloud). I contacted Apple Customer Support and reached a very arrogant rep. He told me that there's no way to backup the full resolution version to a PC. I need to buy a Mac to do that. Is that a nefarious sticky feature Apple uses to keep people on its ecosystem?
The iCloud for Windows app downloads the ‘most compatible’ version of the photo, which is a compressed JPEG capped to roughly 4 MP, as Windows does not by default support HEIF.
You can download the original quality from iCloud.com/photos as HEIF, by selecting some photos and choosing the down arrow at the bottom-right of the download button and choosing Unmodified Original.
Get HEIF Image Extensions by Microsoft on the Windows Store to view HEIC photos and HEVC video on Windows 10.
macOS Photos app always uses the original quality with macOS built-in support for HEIF.
and there's this HEIC to JPEG converter from iMazing to get those 50 GB of photos to the right format.