The unseen (Al-Ghayb) refers to everything that is hidden from human beings and cannot be perceived through their senses, whether it concerns matters of this world, the Hereafter, or anything that Allah and His Messenger have informed us about.
Allah praised the believers by saying:
"Who believe in the unseen."
(Qur'an 2:3)
The unseen includes everything that Allah has informed us of which cannot be directly seen or witnessed.
The answer is: No.
The unseen can be divided into two categories:
This includes everything that Allah has created but remains hidden from people, such as:
All of these belong to the unseen and are created by Allah.
This refers to matters related to Allah, such as:
These are not created, although they are unseen to people in this worldly life.
Some scholars held that Allah is part of the unseen with respect to His servants because they do not see Him with their eyes in this world, even though they know Him through His signs, His proofs, and the manifestations of His power.
For this reason, many Qur'anic commentators stated that believing in the unseen includes believing in Allah, the angels, the Last Day, and everything that Allah has informed us about.
To state without qualification that "all of the unseen is created" is inaccurate, because the unseen includes realities that are not created, such as Allah, His Names, His Attributes, and His Speech.
However, if someone intends only the created aspects of the unseen, such as Paradise, Hell, and the angels, then the statement is correct in that limited sense. It is not correct to generalize it to all of the unseen.
And Allah knows best.