I use the File Explorer Pro App on iPhones and iPads to occasionaly backup all the albums to a NAS. It also has many other useful features i use from time to time.
This doesn’t answer your question directly but iCloud is definitely not the way. Not only it’s unreliable and unusable largely, it is also designed in a way that discourage interoperability.
On Mac (I am aware you have said Windows) So if I were you I’d just dump app the photos locally in normal folder hierarchies (yes drag and drop; not going hunting in Library folder) and then backup wherever you want them. Here’s something https://support.apple.com/en-in/HT205323. Googled it. Absolutely no idea whether it works or how.
Then put something like Dropbox on the job on iOS and it’ll keep uploading your pics and videos which will show up inside one folder on your Windows as well.
My point is — you can’t rely on iCloud after you setup your backup up sync strategy. So get all your data at one point then start your parallel backup/sync setup (and maybe leave iCloud on as well if price is not a concern).
I use https://github.com/icloud-photos-downloader/icloud_photos_do... running on my NAS to regularly download photos from my wife's iCloud account. The photos are stored in full resolution on iCloud with the EXIF data, unlike Google Photos, so that's nice. The only annoyance is that you need to reauthorize the tool every three months. But it sends you a reminder when the time is coming up.
Beware that edits, portraits and some custom photo modes aren't currently downloaded. And modifying an edit twice or more will not sync. (no modtime or chksum)
I was able to backup my iPhone photos (stored on device) to Window using Dokany, ifuse and rclone. This have one caveat though: if you are using iCloud, some of your photos are actually stored as low resolution copies of the original to save space on your device, so original will be not backed up.
