At this point in time there is no way to keep users from creating Flows in the default environment. You can use the Audit Logs in the Security and Compliance center to create an alert that will tell you when they do, but you can't turn off their ability to create Flows.
Hi @NIKOLUCK ,
It is not supported to restrict user from creating new Flow in microsoft flow currently.
Community Support Team _ Alice Zhang
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.
You cannot prevent users from creating flows in the default environment.
Check out the News & Announcements to learn more.
Check out the new Power Platform Community Connections gallery!
Congratulations, the new Super User Season 2 for 2021 has started!
Power Platform release plan for the 2021 release wave 2 describes all new features releasing from October 2021 through March 2022.