Can map files (.mapx) saved using ArcGIS Pro 3.x be imported by previous versions of ArcGIS Pro 2.x?
Are you trying to use these files in a custom print service?
No. Our users send us .mapx files to import into our Enterprise .aprx for publishing for enterprise user use.
No.
Map, layer, reports, and layout files (.mapx, .lyrx, .rptx, and .pagx files) cannot be opened in 2.x once they are created or saved in 3.x.