Hi Leo,
the behaviour is indeed a bit hard to understand. Flow calls itself via the CLI internally when it compiles - we call that a Subrequest (which we’re btw not happy with, and will get rid of, but its still there for now).
To do these subrequests, Flow needs to know which PHP version to use. By default, it uses whatever is exposed as php on the console. If you run Flow/Neos with another PHP version, you need to tell Flow to use that internally as well. Add the following setting to your Settings.yaml:
Neos:
Flow:
core:
phpBinaryPathAndFilename: /usr/bin/php72 #adapt this to your PHP version