I installed Darktable 3.0.1 in Ubuntu 18.04.4 via Software. It installs the Snap version.
But I can't find the print tab (Only visible are: lighttable, darkroom, other, map, slide show).
How to fix printing?
The snap version appears to be missing some features, such as opencl support and printing. Try to remove the snap install and reinstall with sudo apt from the terminal.
3.0 version of darktable should be available from universe for 20.04, for older versions of Ubuntu, to install the latest 3.0 version add this ppa repository:
sudo add-apt-repository ppa:ubuntuhandbook1/darktable
Install Darktable:
sudo apt update
sudo apt install darktable