MOV files not syncing to iCloud Photos from Windows

I am trying to upload pictures and videos to iCloud photos and so far it has been an extremely confusing experience. For years I saved all pictures/videos I took on my iPhone to my Windows PC and recently I have been wanting to transfer these over to iCloud Photos instead of storing them locally.

On my first attempt of uploading pictures/videos to the iCloud Photos website only about half of my photos/videos transferred successfully. For the others I get an error that files must be of JPEG file type. This is a very confusing error message as some videos DID successfully transfer and these are obviously not of JPEG file type because they are videos, so I know this is untrue.

My second attempt to transfer the remaining files was downloading the iCloud for Windows App and copying all the photos/videos into the iCloudPhotos/Photos directory. This successfully transferred all PNG files and about half of the remaining MOV files, but for the remaining MOV files they just sit in the Photos directory with the status "Availability Status: Excluded (not synced)".

My last attempt (found from researching the issue online) was to create a folder within the Photos directory and move the remaining MOV files into this to get them to transfer. On moving them into this subdirectory the green check immediately appeared next to them and their status changes to "Availability Status: Available on this device". However, they don't appear to have synced with iCloud because I cannot find them on the iCloud Photos website.

It's crazy to me how convoluted and difficult this process is and, as a software engineer, I am dismayed by the flaws within this product considering how widely used and established the iCloud brand is. Are there any additional things I can try to fix this?