I just tried a couple of places on desktop and do see the Add photos button. I recommend that you clear the cache for Google Maps and try again. If you’re on a mobile device, you should ensure you have the latest version of Google Maps installed. You could also provide a link here to the POI that you are trying to add a photo to so we could take a closer look.
When you leave a message or reply to someone don’t forget to tag the person so that they will get a notification of your message otherwise they may never know about or see your message. To tag someone, first type @ then type the first few characters of their name until you see their name in the dropdown list. Finally, select the person’s name. You will see that I tagged you at the start of this message to you. Many think that this is done automatically when you reply to someone but it is not.
Also, it’s a good idea if you explain how you fixed your problem as others in the future with a similar problem can search Connect for a possible solution.