Does circularly polarized light change after passing through a lens to linearly polarized light or not circularly polarized light?

No, it's easy to explain, first of all, for you to study polarized light, we ignore the loss brought about by the reflection of the lens (otherwise, to calculate the reflectivity and transmittance of Fresnel on each surface to determine how much each of your polarization component loss, usually we use high-transmittance lens, that is, ignoring the effect of reflection), then you see, the lens this thing, he is not a nonlinear material, usually glass or something, so you, you light through the lens, there will not be any phase change, that is, not circularly polarized light. Usually it is glass or something, so you, you light through the lens, there will not be any phase change, that is, there will not be any chirp, so that it, the polarization state of your outgoing light and you should be the same as the time of incidence. (I hope you've studied crystal optics, uniaxial crystals, biaxial crystals, waveplates, or whatever, so that this kind of thing can cause a phase change and change the polarization state.) But this is the ideal state, but also usually, we can ignore the state, if strictly speaking, due to the thickness of the lens itself caused by dispersion, aberration, and reflection loss and so on, more or less will cause a slight change in the polarization state, but this change is usually negligible!