Yup I just reproduced it by simulating a second screen in the developer options. Cannot open any app that way withoud the device rebooting and crashing.
FIX: hold power button until the power menu comes up and then hold press on the "Power off" option until the safe mode option shows. Reboot into safemode, go to developer options, disable simulate secondary display and reboot again.
You can also boot into safemode by holding "vol -" while booting.