Putting it simply, type 1s basically don't make insulin (or not enough). Providing they inject sufficient insulin for their eating, they can eat what they want without diabetic problems (an unhealthy diet will still cause other problems). If they don't balance the insulin they need correctly, they risk either dropping too low in glucose (hypoglycemia) or going too high in glucose (hyperglycemia).
Type 2s don't have the same problem. We do make sufficient insulin but are insulin resistant. There are two schools of thought about what causes insulin resistance.
One says it's overeating, too much fat and sugar. Based on this, they recommend a low-fat, low-calorie approach with plenty of complex carbohydrates.
Others think it's caused by eating too many carbohydrates, whether simple (sugars) or complex. Based on this, they recommend a low carbohydrate, higher fat diet.
You will see different people with type 2 advocating for one or the other of these approaches. Both have their success stories. Many health care providers believe the first theory and approach are correct. However, they also expect most people with type 2 to get progressively worse, require more medication and develop diabetic complications leading to eyesight problems, neuropathy and possible amputations. Most type 2s on this forum are following the second approach.
Personally, I favour the second theory based on my own experience - I was basically vegetarian for 30+ years, eating a low-calorie, high-carbohydrate diet with lots of healthy fruit and vegetables daily with almost every meal including brown rice, wholemeal pasta, wholemeal bread or pulses. As I developed diabetes, I ballooned in weight without changing my eating habits. For me, weight gain and diabetes followed on from eating what many consider a healthy diet.
Since diagnosis, I have ditched the bread, the pasta, the pulses and the rice. I have increased my fat and protein consumption so that I don't feel hungry. I have lost 12 - 13kg so far and brought my HbA1c down from the 70s to 41.
One lesson to take on board is that we are individuals with different reactions to different foods. Some type 2 diabetics can eat oat porridge for breakfast without it raising their blood sugars. Some can even add a banana to that too. I can't. With a meter, I can check which foods reliably keep my blood sugars stable and those that reliably cause them to spike.