You are right. I think in Full screen Carplay thread
https://x3.xbimmers.com/forums/showthread.php?t=1583913 are some instructions. If not, on newtis you find them.
Payn3y did retrofit the antenna.
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'18 G01 X3 xDrive 30i xLine, Sophisto grey, Vernasca Mocha, Adaptive