We report the results of a muon-spin rotation (μSR) experiment to determine the superconducting ground state of the iron-based superconductor CsCa2Fe4As4F2 with Tc≈28.3K. This compound is related to the fully gapped superconductor CaCsFe4As4, but here the Ca-containing spacer layer is replaced with one containing Ca2F2. The temperature evolution of the penetration depth strongly suggests the presence of line nodes and is best modeled by a system consisting of both an s- and a d-wave gap. We also find a potentially magnetic phase which appears below ≈10K but does not appear to compete with the superconductivity. This compound contains the largest alkali atom in this family of superconductors, and our results yield a value for the in-plane penetration depth of λab(T=0)=244(3)nm.