It is generally not recommended to varnish or apply any type of coating to matt or matte floor tiles to make them shiny. Matt tiles have a purposely non-reflective surface, and trying to add a shiny coating can lead to several issues:
Adhesion Problems: Varnish might not adhere well to the surface of the tile, leading to poor results and an uneven appearance.
Durability Issues: The varnish might wear off unevenly due to foot traffic, creating a patchy and unsightly floor.
Slippery Surface: Varnishing the tiles can make the floor dangerously slippery, increasing the risk of accidents and falls.
If you desire a shiny appearance for your floor, it is better to consider replacing the matt tiles with shiny or glossy tiles that are designed to be reflective and easy to clean. There is a wide variety of glossy floor tiles available in the market that can give your space a polished and shiny look without the need for additional coatings.