Unable to add photos to a FB post

I get your frustration, ** it's not clear to me what you are doing. You say, "absolutely nothing happens," but you don't say after you do what. Are you using the Photos app? Do you use Photos>File>Share, or Photos>FIle>Export? Or are you working directly from a Finder folder? What browser are you using? I'm not a FaceBook user, so it would help if you were more explicit.

If I want to upload a picture to Google images, for instance, I click on the upload link and I am shown a current folder I'm using. Then I go to Photos toward the bottom of the sidebar to select my Photos Library, and I see my Photos Library displayed where I can look through the pictures or search for a particular image. What part of this is not working for you, or what is different?

You need to access the Photos library via the browser while at FB like this:

There is one caveat with Ventura: Albums are no longer shown so you will have to search for the files you want to upload by file name or title or give them a unique keyword and search by keyword.

That's the browser window that appears when you use Safari to upload an image to a website via a "select image" button on the site. This particular site is the Apple site using the Image Insertion button at the bottom of the posting pane. It'll be the same for any website.