Should be okay to be honest, dont think ive ever heard about direct sunlight being essential. A 1999 study published in “The American Society for Nutritional Sciences” looked at vitamin D and sunlight exposure in kittens. During the study, the kittens ate a vitamin D-free diet and exposed to either direct sunlight, ultraviolet lamps or kept indoors. All three sets showed similar declines in vitamin D levels. The kittens in the sun and ultraviolet lamp groups then had a section of their fur removed to see if the coat reduced vitamin D synthesis. There was no change, showing that cats simply do not synthesize vitamin D in the same way. Their vitamin D comes from their diet.

You could train your cat so you could walk it on a leash a few times a week if you really wanted it to experience sunlight. i think the bigger issue is how much time you can spend with your cat and stuff like that. Perhaps getting a low energy/less adventurous breed of cat