This is a weird one...
Okay, let's see if I can explain this clearly.
I have a PSD file open in Photoshop CC 20.0.6.
I want to save the file as a JPEG. So I hit Command, Shift, S and the Save As window pops up.
I go to the Format drop down window and change the format to JPEG.
In the format window it now says JPEG instead of PSD. But, up in the top window the file name still ends in PSD, not JPG. If I hit Save, the file saves as a PSD. I can't change the file format. And, if I try to reopen that new PSD file I get a message saying the file cannot be read and it won't open. I've tried it on a few different images, tried making dupes and saving them, shut down my computer and restarted. I can't figure it out. (And, just in case you're a Genius at an Apple store; Yes, my computer is plugged in and turned on!)
I've been using Photoshop since the mid '90's, I'm not a complete idiot with it. (Well, my wife may argue about the idiot part).
Any ideas? I'm stumped.