I would recommend using the 5.8 kernel given the age of that GPU along with the 340 Nvidia Driver:
First, install Install Nvidia 340
sudo apt install nvidia-340
Switch to 340 in Software & Updates > Additional Drivers tab.
Then install kernel (since both need a reboot after)
sudo apt install linux-headers-5.8.0-63-generic linux-modules-5.8.0-63-generic linux-modules-extra-5.8.0-63-generic linux-image-5.8.0-63-generic
Boot into the 5.8 using the Grub Menu > Advanced Options for Zorin
Ensure you are on 5.8 kernel with
uname -r
Test Steam....