The Yoga of Patanjali is v much dualistic
Its metaphysics is closer to that of Sankhya than it is to Advaita
There are Yoga texts that accept Advaita premises like "Yoga Yajnavalkya"
But Patanjali is more influential
What about the Bhagavad Gita - which is also a Yoga text, in its own right...
The Gita is not just a text of Yoga, but a Vedantic text. But its philosophical position differs based on interpretation
Qualified Monism if you subscribe to Ramanuja's commentary
Monism (Advaita) if you subscribe to Shankara Bhashya
This is in sharp contrast to Patanjali Yoga Sutras, which is unambiguously a dualistic text