Keep in mind restricting group creation also applies to other workloads utilizing Office 365 groups like SP Team sites, Planner, Stream etc.. There is also a AAD P1 licensing requirement for those users allowed to create groups (Teams) ! It’s all in the link
Restricting group creation will not providing solution
For Example: We create a new Team using workflow and assign one new user as Owner, then the 'Join or create a team' link enabled for him, now the new team owner can able to create any number of new teams without following the workflow process.
When you restrict group creation you have to assign a group that is designated as the people who can assign groups. You create a workflow that will add that user to that group then they will be able to create groups / teams going forward.