TQFTs do not detect the Milnor sphere

We show that, under very general hypotheses, topological quantum field theories (TQFTs) cannot detect homotopy spheres bounding parallelisable manifolds, such as Milnor’s exotic 7-dimensional sphere. The result holds for a wide variety of target categories (or $(\mathrm{\infty },n)$-categories) and arbitrary tangential structures. An appendix contains results on the mapping class groups of (stably-) framed manifolds that may be of independent interest.