Black screen flashing and mouse cursor

I had the same issue. its a boot loop, most likely caused by filling the internal SSD to the brim. the way I fixed mine was by using a usb drive installed with a usb bootable Linux distro and I deleted one of my games from the internal drives manually going thru the file system to find it. but an easier way to do it is to just follow the steps here https://help.steampowered.com/en/faqs/vi... and when you get back into steam os clear up some space on the internal drive. only reason I didn't do it the easy way is because the steam recovery image didn't want to boot with my choice of usb drive.