https://9to5google.com/2024/10/18/google-photos-folder-backup/
Please read more at the above link
Every time you visit photos.google.com, Google will look at folders you’ve selected for new images and videos to upload. In concept, this is similar to the Google Drive for desktop app (Mac or Windows).
If this feature is rolled out to you, tap the Upload button in the app bar and select “Back up folders.” This will let you browse your computer to select a folder. Afterwards, you have to “Give Google Photos permission to back up your selected folders.”
Opening that menu again lets you access the “Folder backup” window that shows selected files, which you can remove, and add new ones