Hello Ron60,
Thanks for posting in the Apple Support Communities.
It sounds like you're looking for assistance with Mouse settings on your Mac, right?
If we have that correct, let's see if adjusting the secondary click option will help with this. Check out the steps below for assistance, and you can find more details here: Change Mouse settings on Mac - Apple Support
To change these settings, choose Apple menu > System Settings, then click Mouse in the sidebar. (You may need to scroll down.)
Secondary click
Choose “Click right side” or “Click left side” to secondary click (or Control-click) items on the screen.
In addition, you may be able to adjust the double-click speed to see if that's related to what's occurring. If the mouse is registering two small clicks as opposed to one, this may help to prevent that. Take a look at the details on this, here: Change mouse tracking, double-click, and scrolling speed on Mac - Apple Support
Let us know if this helps with what you're experiencing. If not, confirm which steps you've tried, and let us know which apps are in use for transferring the files. We'll use these details to gain a better understanding of what's occurring, and work from there.
Have a great day!