Thanks for your questions,
On this, mattermost/mattermost-enterprise-edition is the commercial version of Mattermost’s free offering under a commercial license for evaluation, before V11 it required a trial license key in order to evaluate all the capabilities of the platform. With the changes in V11 the vast majority of capabilities around project management, workflow automation and AI agents are available in a rate-limited evaluation mode without a trial key.
Open source users can compile their own version of Mattermost under AGPLv3 license, per Q&A #8 in the V11 changes announcement, or use V11 of Mattermost Team Edition, which remains MIT licensed: Mattermost v11 Changes in Free Offerings
Open source will continue to have security updates. A new Q&A #9 has been added to make this more clear: Mattermost v11 Changes in Free Offerings