Thanks for your reply! By trial and error I found out that the problem was with the arm64 AMX instructions.

Quinn, Is there a possibility Apple may help identifying which particular instructions in the submitted .ipa triggered the ITMS-90755 or this is completely out of question and should/can only be debugged by trial-and-error fiddling with compiler options?

Quinn, Is there a possibility that Apple may help identifying which particular instruction(s) triggered the ITMS-90755 error, or this is out of question and must be debugged by trial-and-error/guesswork only?