I'm working from the Python console in Pro 2.3 and when I importDocument it seems to work but nothing opens. The parameters call for the document and it's layout, so I tried that too. Is there another step that I'm missing?
<SPAN class="keyword token">import</SPAN> arcpy
p <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>mp<SPAN class="punctuation token">.</SPAN>ArcGISProject<SPAN class="punctuation token">(</SPAN><SPAN class="string token">'CURRENT'</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="comment token">#importDocument(document_path, {include_layout})</SPAN>
p<SPAN class="punctuation token">.</SPAN>importDocument<SPAN class="punctuation token">(</SPAN>r<SPAN class="string token">'path\to\MUNICIPAL_LIMITS_A.aprx'</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN></SPAN>There was a similar question to mine here, but it's sort of dated:
arcpy - Importing MXD to ArcGIS Pro programmatically? - Geographic Information Systems Stack Exchange
"To follow up on my comment, the code you posted does work, but does not automatically open the newly imported map."