Does anyone know how to get files to ask to be replaced or skipped instead of it creating a copy of the file? I"m trying to merge files because I have copies of things, but all the Mac does is create a copy no matter what.
I get prompted to choose whether to replace or keep both when dragging a file from one folder to another when the target folder has a file with the same name in it.
I have no idea why your Mac isn't exhibiting the default behavior for dragging/dropping (or copying/pasting) where one or more files that are being moved have identical names to one or more files in the destination folder. Mine works exactly like Bigwaff's does and has for as long as I remember over various macOS versions. Try holding the command or option key down when you drag/drop and see if that bring up the appropriate disalogue that has the "Keep Both / Stop / Replace" options.
That sounds to me like a permissions problem - you don't have write access to the file or folder you are copying to.
Check this out:
On your Mac, select a file that you cannot replace onto, then choose File > Get Info, or press Command-I.
Click the arrow
next to Sharing & Permissions to expand the section.
Click the pop-up menu next to your user name to see the permissions settings.
If you’re not logged in as an administrator, you may need to click the lock
to unlock it, then enter an administrator name and password (or use Touch ID or your Apple Watch).
Are permissions showing Read & Write? If not, change the permissions to Read & Write.