I think I found the solution
The installation should NOT be
Composer (version 2.1.8) successfully installed to: /root/composer.phar
And the installation should be in
cd /usr/local/bin
All settings correct for using Composer
Downloading...
Composer (version 2.1.8) successfully installed to: /usr/local/bin/composer.phar
Use it: php composer.phar
Finally I could verify:
/usr/local/bin# composer --version
Composer version 2.1.8 2021-09-15 13:55:14