have you tried iCloud for Windows? It is supposed to have an option to download all photos at once or by year. (Set up and use iCloud for Windows - Apple Support) I am working on a Mac, so I cannot test with iCloud for Windows.
Alternately, you can use a web browser to download the photos at www.icloud.com. It is easy to select all photos at once at www.icloud.com. Select the first photo, then hold down the Shift key ⇧ and select the last photo of the range, then click the tiny "v" to the right of the download button. The "v" opens a menu to select, if you want to download the high resolution originals or the edited versions. The download will download all photos at once in one compressed zip file. I recommend to download the originals, not the edited versions. Or download both, if you want the edited versions as well.