The Buddha discusses the god Brahma and people denoted Brahmans (and sometimes Brahmins, I'm not clear on the difference, could be just the translator, but neither are the absolute), but not the supreme Hindu Brahman. Was he unaware of this Hindu teaching? Or did he equate it with Brahma? The hypothesis has been
put forth that he was very well aware of Brahman, and that his path to nibbana is the path to Brahman, and that the Tathagata is Brahman, though, considering Brahman is constantly said to be the self and eternal, this would make very little sense since the Buddha declared "sabbe dhamma anatta" (all things are not self, SN 44.10).
Then Brahma Sahampati, having known with his own mind the reflection in the Blessed One’s mind, just as quickly as a strong man might extend his drawn-in arm or draw in his extended arm, disappeared from the brahma world and reappeared before the Blessed One.
SN 47.18, Bhikkhu Bodhi translation
Then Vassakara the brahman, the minister to the king of Magadha, approached the Blessed One
-AN 4.183, Thanissaro Bhikkhu translation
Then Vassakāra the brahmin, a chief minister of Magadha, went up to the Buddha, and exchanged greetings with him.
-AN 4.183, Bhikkhu Sujato translation
Assume all of my words on dhamma could be incorrect. Seek an arahant for truth.
"If we base ourselves on the Pali Nikayas, then we should be compelled to conclude that Buddhism is realistic. There is no explicit denial anywhere of the external world. Nor is there any positive evidence to show that the world is mind-made or simply a projection of subjective thoughts. That Buddhism recognizes the extra-mental existence of matter and the external world is clearly suggested by the texts. Throughout the discourses it is the language of realism that one encounters.
-Y. Karunadasa