Mozart and Clementi's genres were both classical, and played similar music, but both had very distinct and different styles.
Piano TV (https://www.pianotv.net/2017/03/history-of-clementi/) states:
By the end of the 1780s, Clementi was known for his flamboyant, virtuosic style – he performed lots of impressive improv and wildly difficult playing. Later in life he restrained himself a little and developed that refined cantabile style he’s known for today.
Clementi and Mozart both played sonatas, Clementi's music differentiated from Mozart's.
Listen to Clementi's sonata
When you compare both of the musician's sonatas, it is clear that Mozart's famous sonata had a more consistent rhythmic pattern throughout, was repetitive and often included scales. Mozart's sonata was well-constructed, in the sense that every part of his music was connected. It is simple, understandable and familiar (https://interlude.hk/whats-with-mozart/#:~:text=The%20music%20of%20Mozart%20fascinates,%2C%20books%2C%20documentaries%20and%20films.). I thought it was quite catchy, which is why you have probably heard it before.
Whereas Clementi's sonata had a less regular beat. Clementi's music is unique in its own way. It is quite unexpected and relatively more complicated than Mozart's sonata. Clementi's music was unique in its own way For example, from 3:19 to 3:25 of Clementi's sonata, it progresses from fast then to slow, then to fast again. Clementi was probably most recognised for his sonatas. "Clementi’s chief claims to fame are his long series of piano sonatas, many of which have been revived..." - Britannica.
This website (https://www.wolfgang-amadeus.at/en/music_of_Mozart#:~:text=Mozart%27s%20own%20stylistic%20development%20closely,quintet%2C%20and%20the%20piano%20sonata.)
Mozart's own stylistic development closely paralleled the development
of the classical style as a whole. In addition, he was a versatile
composer and wrote in almost every major genre, including symphony,
opera, the solo concerto, chamber music including string quartet and
string quintet, and the piano sonata.
Mozart was unique in the way that he could compose very well in many varied musical formats. Few musicians in history could compose so masterfully in every musical genre. This is probably what made him superior and more famous than Clementi was.
Clementi is less well-known today, but he is known for "being among the first to create keyboard works expressly for the capabilities of the pianoforte". (https://www.classiccat.net/clementi_m/biography.php#:~:text=As%20a%20composer%20of%20Classical,first%20virtuoso%20on%20the%20instrument).
Clementi also admired Mozart's works, but Mozart did not feel the same way toward's Clementi's music, and stated, “Clementi doesn't have a Kreutzer's worth of taste or feeling – in a word, [he is] a mere mechanic.” (https://robertgreenbergmusic.com/mozart-clementi-duel/)