can you upload folders from windows pc to iCloud photos

Yes you can!

One way: Download iCloud for Windows from the Microsoft Store, sign in with the Apple ID you use for iCloud Photos, and enable iCloud Photos in its startup screen. Then it should show up in the File Explorer on the sidebar like an external device. Then you can drag and drop files.

Another way: You can also go to iCloud.com, sign in, click Photos, then choose the cloud with and arrow pointing up. Hope this helps! #Psalm23

This article may help:

Set up and use iCloud Photos on your Windows PC