Not sure this comes under which category. I have tried to install Drupal 7.84 using composer 2.0.9.2 on clean Debian Linux bullseye 11.1.
The directory structure under sites seems little confusing. It is creating the following directories.
web/sites
web/sites/default
web/sites/default/files
web/sites/sites
web/sites/sites/all
web/sites/sites/default
web/sites/sites/default/default-settings.php
...
While installing, it complains that sites/default-settings.php is missing.