In Floorplan Editor, the valid sites for TXN/RXN/MGT refclk are not available for placement (they are still treated as reserved/dedicated).
These pins are not treated as P/N pairs during placement, but they are listed as PTYPE/NTYPE in the Object List.
When will Floorplan Editor support valid sites for these pins?
This is a known issue. It has been fixed in the next generation floorplanning tool.