Locking items inside a frame

@Ana Ximenes - If you only want collaborators to be able to comment, you can set the board’s Share settings to Anyone with the link → Can comment:

More on access rights in this help center article:

https://help.miro.com/hc/en-us/articles/360017572194

NOTE: This requires a paid or Education Plan - you cannot put a Free Plan board in comment-only mode - more on plans and features here.

Because the board is in Comment-only mode, they can’t make any other changes to the board, so you don’t have to lock anything. However, if you really want to,

1. put a frame around the map (press F on the keyboard to get into Frame mode),
2. click-and-drag a frame around the map
3. then press Shift + drag around the map and the frame to select it all
4. and then use the lock button (or Ctrl/Cmd+L)