By default, board thumbnails will be based on the contents of the board. However, you can choose any object on the board to serve as the thumbnail, making it easier to organize and scan through its contents.
To add a custom thumbnail for your board, create an object or multiple objects that you want to use as the thumbnail, then right-click and select “Set as Board Thumbnail”. This thumbnail will now appear whenever you view the board in the folder view or in Slack.
To remove the custom thumbnail, right-click on the object again and choose “Remove from Board Thumbnail”.
Note: