That is an utter mess of self-leveling compound poured way too thick all at once, not fully covering the area, and then not using a proper thinset base. I guarantee the rest of that shitshow is going to go the same way.

That needs to be torn out, the self-leveling garbage pounded out, proper plywood laid in and screwed to the joists for the majority of the space to get taken up, then maybe a thin layer of self-leveling if needed. A layer of Schluter uncoupling membrane can be used to disconnect the expansion of the walls and floor from the tile, with appropriate gaps (like 3/8") around the tile and hidden by the baseboard, with a snap down transition strip at the door that also allows expansion.

And then find whoever installed that and slap the bejesus out of them.