  Over an arbitrary field, we prove that the relative 2-Deligne tensor product
of two separable module 2-categories over a compact semisimple tensor
2-category exists. This allows us to consider the Morita 4-category of compact
semisimple tensor 2-categories, separable bimodule 2-categories, and their
morphisms. Categorifying a result of arXiv:1312.7188, we prove that separable
compact semisimple tensor 2-categories are fully dualizable objects therein. In
particular, it then follows from the main theorem of arXiv:2211.04917 that,
over an algebraically closed field of characteristic zero, every fusion
2-category is a fully dualizable object of the above Morita 4-category. We
explain how this can be extended to any field of characteristic zero. Finally,
we discuss the field theoretic interpretation of our results.
