Subscribe to Shared Album from iCloud for PC Q: How do I use iCloud for Windows to accept an invitation for a Shared Photo Album  without an iOS device or a Mac? 

I have an Apple ID, I can see my iCloud files and photos with a web browser, and I can use the PC iCloud app to upload and download photos but I do not have an iOS device or a Mac.
You cannot subscribe to a shared album without a Mac or an iOS device.

See this message from Apple when trying to subscribe to a shared photo album:


  iCloud Photo Sharing is not available for this device
  
  To subscribe to (sender's name)’s “Sample Photo Album Name” shared
  album on your iPhone, iPad, iPod touch, or Mac, open your invitation
  in the Mail app, and click the Subscribe button in the message.
  
  
  
  To subscribe you need to be signed in to iCloud on:
  
  
  an iPhone, iPad, or iPod touch with iOS 6 or later, or
  a Mac with macOS 10.8.2 or later and iPhoto 9.4 or Aperture 3.4 or later