Fb, IG or WhatsApp can’t access my photos. What’s going on? The only thing I did was delete photos from my iCloud.

When you delete photos from iCloud, any other Apple device that you log in with the same Apple ID, that would have had access these same photos, would find them deleted. This would directly affect Apple apps, not sure about the ones you mentioned ... unless you placed links to them in these same apps.

Did you check Settings>Privacy>Photos, and make sure those apps have been given permission to access your photos?