Every time I save a pic from Facebook I have to go into file manager to obtain, previously this saved automatically into my gallery. I am using a Samsung S8+
"Gallery" is not a location, it is a picture viewing app. The location of the images usually does not matter.
Using your file browser, which folder is Facebook saving your images to?
Is there a file called ".nomedia" in that folder?
Does restarting the phone allow the Gallery app to see the new image?