In all previous versions of the game, a right click is achieved on a macbook/pro by modifying the click by holding the control key. Also known as "Button 2" in control settings.
This no longer works in the snapshot, and there is currently no way to accurately place blocks using a macbook/pro without a peripheral attached.
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Duplicate of MC-13695, please use the search function to see if your bug has already been submitted. Currently over 56% of tickets are being closed as duplicate.