Can one feel the existence of a non-trivial invariant measure?

It is shown that a bounded linear map on a complex separable Hilbert space with non-trivial invariant probability measures doesn’t have to possess eigenvalues. This resolves a question indicated by Flytzanis in 1995 and concretely asked by Grivaux–López-Martínez from 2023 resp. Grivaux–Matheron–Menet from 2021. Still, as a positive result, we prove that every bounded linear operator on a separable complex Banach space for which a non-fixing invariant probability measure exists, has to have some approximate point spectrum on the unit circle minus $1$.