disable cmd+drag to copy clips in project panel, replace with opt+drag
I assume this would be ctrl and drag in Windows. It's extremely frustrating because, if you are trying to select clips, you will often need to click on one hold down cmd, and select another clip that is not in sequence in the project panel eg. clip001 and clip003 but not clip002. Frequently, one can accidentally click off while doing this, that's especially the case with a wacom tablet but happens with mouse as well and because cmd + drag + release is interpreted as copy/duplicate command everytime this happens you accidentally duplicate clips and you have to be very careful to check this hasn't happened without you noticing so you can undo in time before your project becomes a confusing mess.
I have never once copied in this manner on purpose and I doubt a lot of people do because I'm not sure this is even known to be a feature by many apart from something accidentally triggered while selecting stuff. It wasn't until recently that I even realised the cmd key was involved, and only knew that sometimes when selecting stuff Premiere decides to copy it instead.
If this feature truly is useful or people like it, it would be better invoked by holding the opt/alt key as this is less commonly pressed and so has to be deliberately chosen and isn't involved with the more common and crucial project panel task of selecting and moving around clips. There are other functions in Premiere that use opt and drag, however those shouldn't interfere were this behaviour switched to alt rather than cmd because they don't involve the project panel. Frankly I'd prefer that copying by drag simply disappear altogether regardless of what key could instead be used in combination since it can always be achieved much more easily by either using the keyboard, or right-clicking and selecting copy so I can't see a use for it for either heavy keyboard users or people that prefer mouse operation. It just gets in the way.