"Lowkey" as an adjective has been used for a long while and seeped into modern usage. "A lowkey performance" - an understated performance, something that's not gaudy.
As an adverb (e.g. "I'm lowkey in love with Lynn") - meaning "without making a fuss" or "calmly" or "kind of" (all sorts of bringing the intensity down) is more recent, and has been called AAE, but internet speak co-opts it aaaaaaall the time. There's no shoving that toothpaste back in the tube.