Do I lose data when canceling iCloud plan I have downloaded the iCloud photos on my Windows PC through iCloud app and I am able to view the photos in a folder name iCloud Photos in my file browser, but will the photos be still available if downgrade my subscription from 200GB to 5GB? Will I lose all photos and data?
No. Your data won't be deleted automatically when you downgrade your plan. You'd be given a grace period to download your data. Also, the storage decrease takes effect after your current monthly or annual subscription ends.

If you have more data than the space available in your iCloud storage, the excess data won't sync to the iCloud servers and you'd be alerted that you are out of space.