Is there a good app or website where I can input my current diet to check for what might be missing (Vitamins, minerals etc.)
You could use a food tracker, Cronometer, MyFitnessPal, what have you
Unfortunately, it’s not really a good way to see what you’re deficient in. Just because you consume a nutrient, doesn’t mean you’re not deficient in it. There are a bunch of reasons why a deficiency would happen, so for that, you’d have to get a blood test from a Dr
The best way to know if you’re deficient isnt an app, it’s a blood test. A deficiency could be a result of months of underconsuming a vitamin and the app isn’t going to tell you about that, and just consuming the right amount won’t get you out of a deficiency as there are some vitamin stores in your body that takes months to build up to the right levels