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Hi Aaron,
The link to the topic you mentioned in your post is exactly for your case. wrote (I just modified the terms for Mac version):
"Project Manager can only add the Layout (paper space) of a drawing to the Project. If the Layout in the drawing
has not been used, or switched to, and set up, then there will be no "initialized layouts". The solution is to open your drawings, go to one of their layout tabs, and use the page Page Setup Manager (or the Plot command with picking on Apply to Layout button) to set Layout plot settings"
To initialize Layouts in the drawing pick on one of the Layouts tabs I marked on the screenshot and use Page Setup manager to setup plot options. That is what exactly you need to do before adding drawing to the Project Manager.