T-molds are used to transition between hard-surface floors of similar height. the floor does not need to be exact in height to make these work but they should both be hard surfaced floors otherwise the T-mold can break.
They are called a T-mold because they are shaped like a “T”, so if one side is sitting on carpet or another sift-surface floor that does not firmly support the “T” then they can crack over time.
T-molds should not be used in situations where the floors are severely uneven with each other. In this case using a reducer might be better suited to transition the gap between the two floors.