P: Saving copy not saving over jpg file

Argh! You are right!!!! So sorry to get everyone's hopes up 😞

OK, I will try with layers ... report back shortly!

Good point, Philip.

Sophie, try this.

I've been encountering the issue anytime I have layers in my document and am using the Save-As feature to flatten the image to a JPEG, PNG, or TIFF

OK, this is what I'm doing ...

1. Open a new document, CMD + SHIFT + S > test.jpg
2. Open another new document, CMD + SHIFT + S > test.jpg > Replace

The result is test.jpg NOT test copy.jpg

I have also ...

1. Open a new document, CMD + SHIFT + S > test.jpg
2. Open test.jpg and make some changes, CMD + SHIFT + S > test.jpg > Replace

The result is test.jpg NOT test copy.jpg

I've been away from the studio for a couple of weeks sick and my brain is fuzzy. I think this means the problem on my machine is solved though right?

I thought maybe MacOS 10.15.4 would fix it, if not Adobe's fault maybe it was Apple's but no such luck.

I got excited, but I'm not seeing a change. 😞

Hmmm, let me double check this!!!!

Not sure what you are doing differently, but I'm still having the same problem. 

Not sure what is different for you as I'm still having the same issue.