back button & apps button KEYS not working

"Hi!

This is what I've got for you.

Go to Settings > Accessibility > Dexterity and interaction > Assistant menu

From here, toggle the switch to ""ON"". This will create a hovering circle with a window with four panes inside it. If you interact with the hovering circle it will open a new window in which you have access to the back and recent apps buttons via an onscreen button.

Not sure what has disabled the hardware buttons, but this should give you access via onscreen software.

I know it's not a true fix, but a work around."

If it is similar to the j3, the screen is above two sensors that look like small circuit boards. I replaced a screen a while back, and ran into the same issue. I took the screen back off and re installed it. I made sure to line the groves on the bottom of the screen with the small touch sensors. It fixed the problem for me. When installing a screen you should always test it first. You can plug the screen in, turn the phone on, and dial *#0*# this will bring up several test options. The touch test will allow you to test the digitiser, and the subject test will let you test all the buttons including the back and apps button

I have a j5 prime with the exact same issue, I found app in app store called easy home for samsung. It works perfectly, hope this helps