The last supported Vivado release of the XAUI core is version 12.3 (Rev. 6) in Vivado 2019.1.
This core will not be available in future Vivado releases.
The XAUI core can continue to be used in Vivado 2019.1 or earlier and it might be possible to use a core generated in Vivado 2019.1 in later versions of Vivado.
For future support needs, contact Missing Link Electronics: