I believe there was a setting to autofill the purchase date when entering the price. Does it still exist?
If you are adding new movies, go to Tools and then down to Pre-Fill Settings. If you are editing movies already in your collection, I don’t believe this will work.
I’m not sure we ever had “autofill purchase date when entering price” - but what @Yooper1975 says about Pre-Fill Settings: you can add “Purchase Date” to your pre-fill fields, and make it “set to today” when you add new movies.