I have installed QGIS 3.12 through the Ubuntu Store and installed SAGA 7.3.0 through:
sudo apt-get install saga
I tried to install QGIS through
apt-get, as instructed in the documentation of QGIS but this resulted in many errors on dependencies which were impossible to install. I did not run into these issues when installing QGIS from the Ubuntu store.
However, I cannot find the SAGA tools in QGIS. I ticked the activate box in the Processing settings but still, no sign of any SAGA tools in the processing toolbox.
Printscreen of Processing Options