The default behaviour for Lightroom Classic is and always has been to 'Move' folders/files, then delete the files from the original location (see attached screenshot).
Please explain where you're carrying out the moving operation (i.e. within macOS or within LrC). The reason I'm asking is that there has never been a drag and drop option to 'Copy' between disks in LrC. On the other hand macOS drag and drop from disk to disk is actually a 'Copy' operation.
I've just checked on three Mac's and the LrC drag and drop behaviour and still only moves files, which removes to files from their original location.