raspi-config does is add a few lines to
Apparently the latter (128 MB) is the minimum required, and you will get a specific (memory related) error about that otherwise. This comes out of your available RAM.
Check if those are there and not commented out with
#, or superseded by other
gpu_mem (there are a few forms of that, suffixed with with a number, e.g.,
gpu_mem_1024 -- there should only be one) or
start_x values in the file.
Make sure you've rebooted since they were added.
Make sure your firmware and kernel are reasonably up to date:
sudo apt update
sudo apt upgrade
Will do it although it will update everything else at the same time, which you might as well do (I'm not sure what the exact package is). If you've never done that, you should have post install and it may take a few minutes. Alternately, you could use
sudo apt install rpi-upate, then
sudo rpi-update) to pull just the kernel, modules, and firmware but beware this puts you ahead of the Raspbian default and may be a minor gamble. It's never caused me any grief, but the former method (update the system completely via apt
upgrade) is preferrable. You'll have to reboot after this too regardless of which technique you use.
If all that is done and the camera is properly connected, but
raspistill doesn't work, something is busted.