A software project either is or isn't open source. Gitlab CE is source-available (here: https://gitlab.com/gitlab-org/gitlab) with an MIT license, which is a permissive open-source license.
Gitlab CE is open-source. There exist versions of Gitlab with features that require payment. This does not mean that Gitlab (the product) is not open-source; it means that Gitlab (the company) has a core product which is open-source, and then sustains its development through the sale of licenses to product tiers beyond that.
Gitlab CE is open-source. There exist versions of Gitlab with features that require payment. This does not mean that Gitlab (the product) is not open-source; it means that Gitlab (the company) has a core product which is open-source, and then sustains its development through the sale of licenses to product tiers beyond that.