What is Sufism, and is it the same Sufism that Ghazali and Hassan al-Banna followed?

The title of Sufism was given to some ascetics and devout worshippers in the early days of Islam. However, Sufism later became mixed with innovations (bid'ah), extremism, excessive rigor, and polytheistic practices (shirk). Forbidden philosophical doctrines, such as wahdat al-wujud (unity of existence) and the dropping of religious obligations, entered it. Today's Sufism encompasses many deviations, such as exaggerating the status of shaykhs, offering worship at shrines, the widespread practice of innovations like celebrating mawlids (Prophet's birthday) and invented litanies (awrad), clinging to weak and fabricated hadiths, and relying on visions and dreams. Therefore, it is not permissible for a Muslim to follow any Sufi group; rather, one must be wary of them and warn others against them.