Welcome
A quick, and good read about feeding rabbits. It all depends on your options, and what works for you:
https://www.harcourt-brown.co.uk/articles/free-food-for-rabbits
There are several ways to feed rabbits right so that they get old healthy. Fruit and carrots can be a small part of their diet, a very small part, just treats essentially. Rabbits evolved for a meager diet - hay is a good staple food, there are quite good pellets out there, and greens can be a great addition. I, personally, am convinced that a diverse diet helps to avoid problems, but lots of people do perfectly fine with a more convinient approach.
But one of the major points about adjusting diet is: DO IT SLOWLY. Introduce new stuff gradually over the course of 1-2 weeks. And wait until the rabbit is old enough, i would say 4 months or so. Their digestion relies on bacteria, and when new food is introduced they need time to grow the right bacteria to be able to digest it. Rabbits have the instinct to just nibble or ignore new food, that's there to save their lives, mostly because of possible toxins I guess, but if it is too tasty or nothing else available they will eat it and that can cause serious problems.
There is stuff that is more safe than others, high sugar stuff like fruits and carrots should be avoided, only as regular treat once a normal diet is established. Hay is a great, safe staple food. There is a huge difference in store bought food - better avoid colourful mixes and mueslis if possible.
I feed fresh forage, whatever grows on the meadows and along ways whenever available, Pellets as treats, and in winter hay and same veggies. But I'm rather privileged in regard of resources.