Why the soft key of back button works as "Recent button" in Galaxy S8/S8+ device?
This may happen when the “Button layout” option in “Navigation Bar” setting is changed.
If you want to change or recover the order of soft keys,
Please tap the Setting → Display → Navigation bar → Button layout and then select the order which you want.
Pictorial representation of the above settings are as follows :
1. Tap Setting.
2. Tap Display.
3. Tap Navigation bar.
4. Tap Button layout.
5. Select the order which you want to change.
6. Now the order has been changed.