Hello I_hate_Zip_Files,
It sounds like you are seeing all the photos being downloaded from iCloud saved as zip files, right? Do these include new and old photos? How large are these files typically?
Does it happen with just one browser or have you tried different types of browsers?
Download iCloud photos and videos - Apple Support
"On your Mac or PC
- On iCloud.com, click Photos and select a photo or video. Hold the command key on your Mac or control key on your PC to select multiple photos or videos.
- Click and hold the download button
in the upper corner of the window. If you want to download your photo or video as it was originally captured or imported, choose Unmodified Original. For JPEG or H.264 format — including edits, and even if it was originally in HEIF or HEVC format — choose Most Compatible.* - Click Download.
If your photos download as a ZIP archive, learn how to uncompress the folder on your Mac or your PC. "
Regards.