How to periodically back-up iCloud photos on external device?

Hello everybody! I‘m new to the Apple world and looking for advice. I‘m using iCloud to sync the pictures taken by my iPhone. To have a physical backup and save space in my iCloud plan, I want to periodically move/archive older photos from my iCloud to an external drive or NAS. How can I do that?

In a perfect world, I was looking for a workflow like this:

1. Download all iCloud images in original quality (to my Windows PC or MAC) while retaining the album structure (such as „vacation 2025“).
2. Copy those original images to my external drive (except for duplicates already stored on there).
3. Remove old pictures from my iCloud to save space, i.e., only keeping the pictures taken during the last 6 months.

Does anybody know how to solve this? Does my desired workflow even fit the Apple cosmos?