I want to know about guru gobind singh and their real philosophical and spiritual writings as dasam Granth seems to have some hindu ideology which guru giving singh g can't write he must have his own writings as well?

Guru Gobind Singh Sahib ordained Guru Granth Sahib as ever living Guru, in October, 1708, at Nanded. Guru Nanak Sahib, in his discussion with Yogis, had made it very clear that his Guru was Shabad. Therefore, whatever is included in Guru Granth Sahib is Guru.
Guru Gobind Singh Sahib could have included any of his writings in Guru Granth Sahib and given the same, the status of Guru, which he didn’t do. Therefore, it is not clear as to what he wrote. In view of the position it is difficult to say what he wrote.