The CLI PHP Composer extension command below fails with an error:
# plesk ext composer --application -list
Call to undefined function PleskExt\Composer\Cli\create_function()
Plesk PHP Composer extension bug with ID #EXTPLESK-4427 which will be fixed in future extension updates.
Until the bug is fixed as a workaround:
Find the applications list at Domains > example.com > PHP Composer