What is the ratio of cosmic microwave background radiation to normal radiation?
Photons from the CMB outnumber all other photons by more than 200:1.  This is contained in Pela's excellent answer to: Does the number density of photons  nγ≈108m−3  refer to CMB photons only?.  Pela uses this graph from Hill et al. 2018 to derive this ratio.  Note that the CMB forms the largest contribution to the electromagnetic spectrum.