Hello SaritaMc,
Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with uploading 1 photo to iCloud due to an incorrect file type. This article goes over the supported file types iCloud uses: Set up and use iCloud Photos
"File types that you can use with iCloud Photos
Your photos and videos are stored in iCloud exactly as you took them. All of your images are held in their original formats at full resolution — HEIF, JPEG, RAW, PNG, GIF, TIFF, HEVC, and MP4 — as well as special formats you capture with your iPhone, like slo-mo, time-lapse, 4K videos, and Live Photos."
If you're using the iCloud website, only JPEG images may be uploaded as mentioned here: Upload and download photos using iCloud.com - Apple Support
"You can upload JPEG images from your computer to your Personal Library using iCloud.com."
The file may be labeled incorrectly and need to be converted into a compatible file type to work.
We hope this helps.
Cheers!