See if it does it in safe mode:
go to settings/update & security/recovery
under advanced startup, choose restart now button
this will restart PC in a blue menu
choose troubleshoot
choose advanced
choose start up options
hit the restart button
choose a safe mode (it doesn't matter which) by using number associated with it.
Pc will restart and load safe mode
see if backspace works here. If it does, its likely a driver problem... if it doesn't, i will have to think about it.
What make/model laptop is it?
resetting keyboard may work but only if its a driver problem: https://www.wikihow.com/Reset-a-Keyboard