Bro if it is not getting added in Game launcher , Because if you are playing PUBG for long time, due to overheating it may reduce the performance... To play PUBG without lagging, I prefer you not to play under Game launcher...
if not added into game launcher goto settings --> Apps find game launcher and clear cache and came back to home screen now your Pubg added into game launcher
bro did you download pubg from stores or get it through sharing apps cause sometimes game launcher doesn't take it as game if you get pubg through xender or share it however I am seeing that error msg (" PUBG isn't a game ") first time
