The packages like

• ezsystems/ez-support-tools,
• ibexa/post-install,
• ibexa/installer

use Composer 2 feature(s), e.g. Composer\InstalledVersions but it's still possible to install the Product using Composer 1. It will however fail later on, which gives bad DX.

The solution is to include composer-runtime-api:^2.0 in require section of those packages.