"Woke" or "wokeness" generally means that work has progressive themes, like pro-LGBT, anti-capitalism, "DEI" cast/staff, ETC. Undertale in particular I guess would be the presence of some queer characters/interactions, though the non confrontational gameplay could be perceived as woke as well

I mean it's just a couple of gay people and a trans robot it's not that crazy. Not sure what's so woke about spreading kindness in pacifist either. I'm quite tired of people associating basic human kindness and respect with politics