How to generate lightmaps for 3d models in unity?

I have tried to generate models from online resources like sketch fab and other platform, but unity is not able to produce lightmaps for them, I simply don’t understand why that is not working. When I click on the generate lightmap uvs on import setting, in unity it say importing and get busy and the countdown starts and it goes on for hours but it never gives me the models with lightmap. Please help me with all the possible setting so that I am able to generate them. Or atleast help me understand what I am doing wrong here. I am using 2022.3.8f1 LTS version.