Well it technically started with Soulja boi in 2007 and then Kanye making 808s and heart break in 2008 which inspired zoomer children all over the world. But it really came into mainstream with Waka Flocka flame in 2010. Then in the early2010s artists line migos perfected the normalization of The trap and Mumble rap sound. Kanye again released an album in 2013 that was full fledged autotune trap psychedelic hip hop that people thought was weird but then Travis Scott became mainstream with the same sound. Artists like young thug, lil Uzi vert and 21 Savage basically normalized the autitune sound or Mumble slow rapping to the point where lyrical sounding hip hop sounded old and for has been boomers from another time. Nowadays wen you have a rapper who raps lube JID they are really the odd one out, not popular and part of a niche genre.
I think autone Mumble rap has paved the way for other"rap" sub genres like emo rap, wreck which had replaced the Linkin parks and breaking Benjamin's for zoomers. Look at Lil peep xxxtentaxion and juice world. Weird they are all dead too. But nowadays the rapper voice just has to sound cool and have swag on the melody
Call me crazy but I think lil Wayne, Kanye West, Waka Flocka and even Soulja boy are the leaders of this new trap/autotune/mumble rap era. Like they paved the way she artist like migos and Travis Scott could become the new norm