lock boards for team members

Hi @Ulrike! Are you on Free Plan? 

Because on Free Plan, all invited users are automatically added to your team and get access to all boards. Here's some more information on sharing access:

https://help.miro.com/hc/en-us/articles/360017730813-Sharing-boards-and-inviting-collaborators

@Ulrike - Because you are showing a Project, you are definitely not on a Free Plan.

Even though you have disabled the Project’s Anyone in your team can view this project setting, you will also need to adjust each board’s Team permissions:

Set to No access if you do not want the team to be able to see the boards at all.

NOTE: If you have the Visitors/Anyone with the link access set to anything other than No access, they still won’t be able to see the board, but they could access it if they had the link.