Guru Gobind Singh ji in all his wisdom bestowed Guru-ship on the Bani enshrined in Sri Guru Granth Sahib.
All Sikhs followed Guru Gobind Singh ji’s Hukam till some anti Sikhi forces introduced Bachitar Natak, now titled Dasam Sri Guru Granth Sahib. (Commonly called Dasam Granth).
The Bachitar Natak (Dasam Granth) does not follow the norms of Bani of Sri Guru Granth Sahib. E.g. use of Nanak in every sabad.
And for multitude of other reasons it can possibly not be the writing of the Dasam Jot of the Guru Nanak.
For those who believe it is the writing of Guru Gobind Singh ji, please note: it is playing the role of Prithi Chand, son of Guru Ram Das ji and elder brother of Guru Arjan Sahib ji. Sikhs know well the role of a very negative and harmful sareek played by Prithi Chand and his next generations.
Sikhs need to use Bibek budhi and stay focussed on the message of SGGS Bani.
A Sikh may read any and all other writings but none of them is Sikhi Guru.