upgrade – How to solve Magento 2 with composer 2 version error when sample data install

I am not sure which m2 version are you using, but the magento tech stack documentation state that m2.4.2 is compatible with composer 1.x & 2.x, however, m2.4.1 is compatible with only composer 1.x. So upgrading composer while using 2.4.1 is a big no-no.

Even if you get this warning, this is unlikely that it’s the reason why the installation failed.

Try adding the sample data by running the following commands:

bin/magento sampledata:deploy
bin/magento setup:upgrade

(Source https://devdocs.magento.com/guides/v2.4/install-gde/install/sample-data-after-composer.html)

Good luck!