Absolutely recommend The Left Hand of Darkness! I loved it and it was possibly the only book to move my husband to tears. It explores gender both as a social construct and as a biological truth, as well as love across cultures.

Everything by Le Guin is gold, honestly. I particularly loved the fourth Erthsea novel, Tehanu, on gender discrimination. And The Dispossed, discussing exile. As an expat/immigrate, it resonated deeply with me.