Join Teams work meetings from Microsoft Teams (free) and vice versa

Microsoft Teams (Free) users can currently join Teams for work (or school) meetings only as guests, which requires them to use a browser and results in a sub-optimal experience. The new feature rolling out will allow these users to join Teams for work (or school) meetings in one click, without being redirected to the browser or asked to fill in their name/surname. They will also be able to continue collaborating with the meeting organizer and other participants via meeting chat after the meeting.  The feature will work in the opposite way as well, so Teams for work (or school) will just as easily be able to join meetings hosted by a Teams Free user with one click. This is associated with Roadmap ID: 167326

What is Microsoft Teams Exploratory Experience and can you manage it?

Microsoft Teams Exploratory experience is a great feature for users without a Teams license to get to know Teams, and get involved with other organizations already migrated to Teams. The Microsoft Teams Exploratory Licence will replace the Commercial Cloud Trial license available today.
If a user has already been assigned a Teams license, the feature will not be available for that user (Also, the feature is not available for GCC, GCC High, DoD or EDU customers).

If, for some reason, you do not want your users to start playing with this experience (Let's say you are not ready to support the features, or you want an absolut controlled migration from SFBO to Teams, as many of my customers like), there are a couple of ways you can manage this.

The only way to turn this feature off completely, is to globally disable the use of trial apps and services. This can be done under the M365 admin center and "Services & add-ins", provided the organization is eligible in the first place.

If a user have already been playing around with the feature, the licence will have to be removed in M365 admin panel where all the user's licences are managed.

I highly recommend reading the documentation here if this is something you need to look into.