It is a well-known hairstyle that many people go for. Is it allowed in Islam to have this type of haircut? In the narrations of the Prophet (ﷺ) we see that it is forbidden to shave a part and leave a part.
With a high, low or medium fade, the sides are shaved away. The top portion of the hair is often left longer, and this belongs to al-Qaza'. Al-Qaza' is to shave off one part and leave another part.
Ibn 'Umar narrated: "The Prophet forbade al-Qaza'." [Sahih al-Bukhari 5921]
The alternative to the well-known overflow is to trim or cut the hair. It is also possible to shave the hair completely short or leave it long.