Einstein won the Nobel a hundred years ago proving that light works in chunks called photons. If a photon needs frequency v to ionize an atom, then you can shine frequency v/2 on it for years if you want — it will never ionize the atom. This is because the energy from the lower frequency light doesn’t “build up” in the atom until the electron is kicked out. The photon must have the correct amount of energy needed to interact with the electron and eject it. Otherwise, nothing happens.

So it might be true that the overall radiation exposure from WiFi in terms of total energy might be equivalent in a few years to solar energy received in a few minutes, but the physical impact is not equivalent. Sunlight contains ionizing radiation (hence sunscreen) while WiFi routers do not emit ionizing radiation. You can sit next to a router for your whole life and it will be fine. Maybe if you had a super powerful router, you’d start to worry about thermal radiation since WiFi sits in the microwave part of the spectrum.