when i presss back button it shows option to clear recent apps..
bro just swap the buttons on settings
yeah even I'm facing this issue many times
You probably have what you call the "back" button programmed as "recent. As previously stated in this thread, swap them. And for the love of God, don't ask how to do so.
please check with your settings in button
long press action and double tap action
moreover you have to confirm whether you are using original tempered glass
Device Trees and Kernel Sources for OnePlus 5T
by Adam Krisko, 2017-11-17