I want to use the plugin to build a compatibilityMode app , so - it should not install any node on the system, or why does it still need npm?

Configure project :
Using DS Gradle Vaadin Flow Plugin 1.3.5 (UNLICENSED). Hide this message using --quiet with PRO subscription.
vaadin.version is not set, falling back to latest Vaadin version
The project will be compiled for Vaadin 13 (Flow 1) compatibility mode. Running in NPM mode is only available for PRO subscribers.
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:nodeSetup