Hi and welcome.
Part of the confusion is because diabetes can be highly individual and partly it is because old school NHS advice is a bit behind the curve. What we recommend here is finding what works for your body by measuring it. This involves getting a Blood Glucose home testing kit and taking a reading immediately before eating and then 2 hours after. You are looking for the post meal reading being no more than 3mmols higher than the premeal reading. If it is, then test that meal again.... just to be sure because bodies are not always consistent in how they respond, and if you still get a high reading afterwards, then reduce the amount of carbs in that meal and test again, until you find the proportion/quantity that your body can cope with. A lot of it depends on your digestive system and metabolism. So for instance porridge is supposed to be slow release (low GI) but my digestive system breaks it down nearly as quickly as sugar, even when I use minimally processed jumbo oats to make it and water and cream instead of milk (cream is lower carb that millk and the fat from the cream should slow the release of the glucose from the oats..... but no, not for me 🙄 ) Of course it was standard NHS advice to opt for porridge as a diabetic but it certainly doesn't work well for all of us. My digestive system also breaks down lentils and chickpeas much more efficiently than it should so I have to restrict those too, but my BG 0meter clearly shows which foods cause me problems. Apples send me high so I have to have half an apple one day with a chunk of cheese and the other half the next, but I am OK with an apricot or a kiwi. It certainly isn't just about sugar as many people are led to believe. All carbohydrate gets broken down into glucose, so foods high in carbs like grains and grain products (bread, breakfast cereals, pasta, couscous etc) and starchy or sweet underground veg like potatoes, sweet potatoes, parsnips and carrots and fruit need to be carefully monitored and portions reduced in line with what your particular body can tolerate.
It may seem really complicated and mind boggling at first but one you get into the swing of testing, and keeping a food diary, you start to see patterns and learn what works for you and what needs to be kept as a special and occasional treat or what is simply not worth the BG upheaval like porridge for me. I love chickpeas and lentils so I have a little treat with those occasionally.
Anyway, good luck with your follow up test..... perhaps if your levels are borderline you might manage to bring your levels down a bit by implementing some changes now and dodge a full diabetes diagnosis. Even if you bring your levels down the pre diabetes levels, you will still need to make some dietary changes to prevent it rising, so no harm in getting into the swing of it now.
If you intend to self monitor with a home kit, the cost of the test strips is the most important factor when self funding as you get through a lot of test strips in the first few months until you build up a repertoire of meals and portion sizes which your body can cope with, and test strips are not universal, so getting a meter which has the lowest cost strips is an important consideration. The 2 meters most frequently recommended by people who self fund on the forum for econo,my of use and reliability are the Spirit Tee2 and the Gluco Navii.
If you have any questions, just ask. It is a lot to take in at first and it can be a bit overwhelming, but gradually it all starts to make sense. Weighing or measuring portions of some high carb foods like breakfast cereals or the amount of porridge oats you use to make your porridge, is helpful until you get an eye for portion size.