During the upgrading to stretch:
"This system has a graphics card which is no longer handled by the
NVIDIA driver (package nvidia-driver). You may wish to keep the package
installed -for instance to drive some other card - but the card with
the following chipset won't be usable:
01:00.0 VGA compatible controller [0300]: NVIDIA Corporation GT218
[GeForce 210] [I0de:0a65] (rev a2)
The above card requires either the non-free legacy NVIDIA driver
(package nvidia-legacy-340xx-dnver) or the free Nouveau driver (package
xserver- xorg- viaeo-no^veau).
Use the update-glx command to switch between different installed drivers.
Before the Nouveau driver can be used you must remove NVIDIA
configuration from xorg.conf (and xorg.conf .d/).
Install NVIDIA driver despite unsupported graphics card?"
I