In your comment you stated that you installed TeXLive (TL) via the Ubuntu repositories. However you are using Ubunto 18.04, which ships only TL2017 in its repositories (see https://packages.ubuntu.com/bionic/texlive). Therefore by executing
sudo apt-get install texlive-full you are installing TL2017 and not TL2020.
If you want to install a more recent version of TL (independent of the Ubuntu repos), you will have to do it manually. But no worries this is not a big deal. The process is described at http://tug.org/texlive/quickinstall.html
Essentially it boils down to:
- Download the zip from http://tug.org/texlive/acquire-netinstall.html
- Extract the zip
- Run the
install-tl script (if I remeber correctly you'll want to run this script as sudo in order for it to be able to install TL into system directories)
- Adapt the configuration of TL interactively via the script
- Let the script install TL (this will take a while for it to download all files to your computer)
Note: You might want to uninstall the TL version from the Ubuntu repos before performing above steps. For that check this answer.
EDIT: If you only want to update TeXStudio and continue using the TL version you have already installed, you can install a more recent TeXStudio version via their PPA repo. The process is described here: https://ubuntuhandbook.org/index.php/2021/02/texstudio-3-0-5-released-install-official-ubuntu-ppa/