It could be an evolving area to move files across libraries, however doing some testing

The option to unselect move of permissions appear only when one file is selected to be moved to a different SharePoint site. The option does not appear for bulk moving or moving of a file to a different library within same site.

What happened to the unique permissions on the moved files when there is no option to uncheck move of permissions

Move of file to a different library in same site - without unique permissions : moved files inherit permissions from library Move of file to a different library in same site - with unique permissions : moved files retained permissions from source, i.e. sharing links and direct access are carried across Bulk move of file to a different library in same site - without unique permissions : moved files inherit permissions from destination library Bulk move of file to a different library in same site - with unique permissions : moved files retain unique permissions Move of file to a different library in different site - with unique permissions/: if ‘keep sharing with same people is unchecked , the permissions are not copied across, else unique permissions are copied across if checked. Move of file to a different library in different site - without unique permissions: if 'keep sharing with same people is unchecked or checked , the permissions are not copied across Bulk move of file to a different library to different site - without unique permissions : moved files inherit permissions from library not carrying across the unique permissions settings , e.g. sharing links Bulk move of file to a different library to different site - with unique permissions : moved files inherit permissions from library not carrying across the unique permissions settings , e.g. sharing links