These are more accessible modern works that point you to more classical works if you're interested:

Tantra Illuminated by Christopher Wallis

Roots of Yoga by Jim Mallinson

Three Pillars of Zen by Philip Kapleau

The World of Tibetan Buddhism by the Dalai Lama

People like to recommend the Heart Sutra and Pali Suttas, and Bhagavad Gita but I'd say it's better to get some intro first so you can at least become aware of any prior assumptions you have about the world and realize those works come from a wildly different experience of being.

Bonus: Dark Emu by Bruce Pascoe The Hermetic Tradition in African Philosophy by Theophilus Okere Spell of the Sensuous by David Abram