[Translated]: I can't cut the object normally, instead I have a polygon. How can I fix this so that it no longer exists?
I think the problem is that particular face already has more than 4 verts before you attempt the cut. Blender prefers quad-based toplogy, so loop cuts don't work as expected on n-gon's (faces with more than 4 verts. Make sure the face you're trying to cut has only 4 verts
Start by joining these two vertices (Select and press J):
Then select these three edges, Right-click and select "Subdivide":
x> dissolve $\endgroup$