Miro help says: 
How to duplicate a Miro board To do that right from the board click the name of the board in the upper-left corner and you will see its info card and the option to Duplicate : 
 
Not true - on this board there is no DUPLICATE button…
 
Help also says:
To duplicate a board from the dashboard open the board context menu or right-click the board icon and choose Duplicate : 
 
Again  - NOT what I see, on the board I wish to duplicate the board contect menu has no DUPLICATE choice...
                 
     
                                    
            @David Fangman  True:
Source: https://help.miro.com/hc/en-us/articles/360017730113-How-to-duplicate-a-board 
The board owner can chose who can duplicate the board, effectively duplicating the board’s content.
To demonstrate this, here is a board that resides in my Consultant Plan team that is set to Anyone with the link → Can view :
The the Board content Settings are set to Anyone with the board access: 
 
 
The results is that you can open this board, click on the board name, and duplicate the entire board to a team that you are a member of:
https://miro.com/app/board/o9J_kl4Sue4=/ 
Board Content Settings In order to obtain a copy of the board you are looking to duplicate, you will need to contact the board owner and as them to adjust the board content settings  as I have shown above.
Or, if you are a member of paid or Education Plan, you could ask then board owner to send you a copy of the board in .rtb format and then you could restore the board to your account.
More on this here → https://help.miro.com/hc/en-us/articles/360017572774-How-to-save-board-backup