Ubuntu Install 20.04 LTS

 install composer

apt update

apt install wget php-cli php-zip unzip

php composer-setup.php --install-dir=/usr/local/bin --filename=composer
Output
root@vps:~#  php composer-setup.php --install-dir=/usr/local/bin --filename=composer
All settings correct for using Composer
Downloading...

Composer (version 2.3.5) successfully installed to: /usr/local/bin/composer
Use it: php /usr/local/bin/composer
To test your installation, run the following command.
composer