I can't upload photos from Photo to internet sites

Hmm. That's a Finder sidebar. We can tell this simply because it has a Tags heading and no Media heading. So, basically, as we've been telling you, you're looking in the wrong place. So, try this now.

You're reading this in a web browser. Go command-o. (That's a command to open a file. It results in a dialogue box - so called as it's the way the computer asks you what you want to open). Can you see the difference in the sidebar?

On the left hand side of the window, do you see the scroll bar? That means there is material, lower down, out of sight. Is there a Media heading there? And is there a section in the called Photos? What do you seen when you click on that?

There is no media heading (screenshot). I should say that I had trouble with Catalina (disaster really) and the Apple advisor had me essentially wipe my hard drive, install Mojave, and then reload my data (including photos) from my external My Passport. I don't use iCloud if I can help it....the computer seems able to access the Photo Library (which is greyed out, meaning it's selected) and roll random photos as a screen saver...and if a photo is on my desktop I can upload it, either to a site like Facebook or to another program on my hard drive...before the disaster, sites like Facebook were able to pick up photos from the Photo Library...some kind of linkage or setting seems to have gone wrong...and...where can I find that Media heading? Thanks for your help.

Oh HEY!!!! Thank you! We are really kind of duh, duh, duh out here...So that was it...just not scrolling down far enough and somehow thinking "Pictures" meant ...well, pictures :). Thank you again, Terence!