No. There is no browser version of GTA 5, and any site claiming one is either lying or streaming.
GTA 5 is roughly a 100GB modern game. There is no WebAssembly port, and there will not be one, because the asset size and the engine complexity make it impossible in a tab.
What does exist is cloud streaming. Services like GeForce Now and Xbox Cloud Gaming render the game on their hardware and send you video. That is not a browser port, it is a rented PC, and it requires a legitimate copy of the game on a supported store.
Anything else advertising GTA 5 in your browser is bait for a download you do not want.