Earlier quoted context omitted.
Open source doesn't just mean that the source is publicly available, either, though. This definitely isn't an open source license: https://gitlab.com/gitlab-org/gitlab-ee/blob/master/LICENSE
Why not? You can modify/redistribute it, you can't just deploy it to production without having a valid subscription. It's not Free Software, but it is Open Source.
If you cannot deploy it without a paid subscription, it's not Open Source by most commonly accepted definitions of the term.
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[0] https://www.gnu.org/philosophy/free-software-for-freedom.en....