'Freeze Boards' can be accessed via the dropdown menu that is part of the top bar menu item for Boards for those with the 'Board Host Controls' activity in their session role.
Clicking 'Freeze Boards' removes all of the hover over menus for boards and makes the boards inactive for those without the 'Board Host Controls' role i.e. students.
Putting the boards into freeze is a great way to help manage students attention and allows the teacher to interact with boards during and briefing activities while making them inactive for students.
If the students want to put the board into 2D mode for viewing while the boards are frozen they can right click on the board and choose the '2D View' option.
Boards will remember any previously locked states when coming out of freeze.
Boards are also automatically placed in freeze as part of 'Holding Mode' when a teacher isn't present.