If you installed your TeX distribution via
apt-get, then you can get
biblatex by installing the package
sudo apt-get install texlive-bibtex-extra
LaTeX packages are usually available in the
apt repositories not separately, but grouped into collections.
biblatex is contained in the
You can find out which collection contains a package you are looking for by searching for the
.sty file in the package contents: https://packages.ubuntu.com/search?mode=filename&suite=focal§ion=all&arch=any&keywords=biblatex.sty&searchon=contents or https://packages.ubuntu.com/search?suite=focal&arch=any&mode=filename&searchon=contents&keywords=biblatex - obviously you have to pick the right Ubuntu version, I chose Ubuntu 20.04 LTS [Focal Fossa] in the example.
Note that the TeX distribution you get from
apt-get on Ubuntu (and similarly for other Linux distributions) is usually frozen and does not receive any updates. After a while, those distributions can get outdated, especially on LTS releases.
For example Ubuntu 20.04 LTS (Focal Fossa) has a TeX live 2019 packaged in February 2020. The current TeX live is TeX live 2021, which receives daily updates. So you would be about 18months behind current development.
People who want to receive bug fixes in TeX packages and who want to benefit from current development are usually advised to install "vanilla" TeX live from TUG.org: How to install "vanilla" TeXLive on Debian or Ubuntu?.
With a vanilla TeX live, you'd install
tlmgr install biblatex
sudo tlmgr if you need super user rights to run