I just upgraded to Audacity 4 and all of the aup3 files in my downloads folder are gone. Every single one of them. All deleted. I installed on the same drive, and this happened.
Even Audacity4 is not capable of doing that.
Could be your AUP3 files are not associated with Audacity4.
Audacity4 should be able to open AUP3 projects, but will save them as AUP4
Nevermind. I got the search term wrong.