P: Saving copy not saving over jpg file

no, it doesn't. At least not for me and the bug isn't mentioned in the release note either.

I just did the 21.0.3 update, and it didn't change a thing for me.  Still making copies instead of overwriting/replacing files.

21.0.3 seems to have fixed the copy bug!!!!

I think I just stumbled upon a workaround fix!! If you use the "Save For Web" feature it seems to actually overwrite the file rather than saving it as a copy.  Let me know if this works for you!!

File > Export > Save for Web

I think I just stumbled upon a workaround fix!! If you use the "Save For Web" feature it seems to actually overwrite the file rather than saving it as a copy.  Let me know if this works for you!!
File > Export > Save for Web

The screen share and permissions remedy does not work. I've done this w/ Adobe tech support already. In the end, he said they knew it was a known issue and will be fixed in an upcoming update (obviously not the last one!

I think it is an OS problem - Catalina. I have Catalina on my MacBook Pro and it started happening when I updated. On my desktop, I haven't updated yet and it's fine. 

Supposedly, if you get Adobe tech support and share your screen, they do something to remedy the situation - most likely delete and/or edit a file in the Library->Adobe folder. If anyone has done this, would like to know, this remedy should be posted ONLINE for ALL TO SEE. It has to do with permissions - it is related to the same issue that greys out all of the filenames in dialogue boxes. Adobe apps, for some reason, getting hung up on the Catalina update. Why they can't release an update to this is mind-boggling given the size of the user base they are pissing off. Thanks.

Yes, this is 100% on Adobe. When half your client base is using a certain OS, you absolutely have to ensure you stay compatible with it. This isn't Apple's fault.

I would say the burden falls on Adobe as it is (apparently) a compatibility issue with the latest OS. Rarely (if ever?) will you find an OS release fix to accommodate a 3rd-party application, but the other way around. Cheers!