danclarkie If you want to run composer with a different version of PHP, then you can do that by passing the composer executable to whichever PHP version, like so:
php81 <path to composer> <your commands here>
You can also run the following commands on the server via SSH:
mkdir -p ~/bin
ln -s /usr/bin/php81 ~/bin/php
export PATH=$HOME/bin:$PATH
That will create a "php" executable symlink in your ~/bin directory linked to php81. The PATH setting will make it the first "php" on the search path, i.e., when you run "php", it will use that instead of the system default.