Installation on Ubuntu of qgis
On the latest Ubuntu long term support release (20.04) the LTR long term support version of qgis 3.10 was added. If you are a company looking for long term version of gqis installing qgis from the default ubuntu repositories might not be such a bad idea.
If however you want to install a more recent version of qgis (either latest release or a more up to date LTR version) or possibly are using an older ubuntu version you will need to install qgis from the official qgis repositories.
For smal teams / people happy doing software updated we recommend using the latest version (3.12.x) and this is what this quide will help you doing.