I'll actually answer this question.
GTA 6 will come out 2022-3 earliest.
GTA 5 came out in 2013 and Red Dead Redemption 2 came out in 2018, five years after release. Though RDR2 was announced in 2016 so at least GTA 6 should be announced a couple years before.
Before GTA 5 came out R* released one game a year but because GTA Online made so much money they were able to justify taking more time to release their next game. GTA Online is still making money to this day so I expect them to take the same amount of time if not more to release GTA 6.