This is the issue - I have no idea currently what is good bad or indifferent.
I’m still in the early stages of understanding so basically clueless
It is a steep learning curve.
Let your meter tell you what is good, bad or indifferent, alongside a food diary. Have you started your food diary? If so, what portion of Bran Flakes did you eat, and how much milk (and which sort of milk) did you pour over it? These are the sorts of things you need to write down in your diary. It may involve some weighing at first so you know exactly how much of it you are eating. If the food is countable, such as strawberries, just count them. If it can be measured in a tablespoon, measure it. etc.
The main foods to cause us all problems are breakfast cereals of all kinds, bread, pasta, rice, potatoes, fruit, pulses such as beans, anything made with flour or containing grains. That isn't to say you can never eat these things, but your meter and diary will help you with portion sizes - and it may be you have to eliminate some completely.
You are safe with all meat and fish (but not if it is coated), bacon, eggs, dairy foods, most but not all vegetables, mushrooms, and a whole host of other stuff. Basically, real foods and not processed stuff. This list of foods will give you some idea.
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https://www.dietdoctor.com/low-carb/foods#foodlist
This website is informative
https://www.dietdoctor.com/low-carb/60-seconds