Nakd bars are worth a look, they're smoothed nuts and dates for the most part, so whilst they don't contain any refined sugar they are still pretty carbohydrate intense because of the dates, they range from 12g of carb through to 17g depending on the flavour. They don't spike my blood sugar but I tolerate dried fruit very well and some don't, I know someone who eats dried fruit to treat hypos and I'd have passed out before they made it through my stomach 😱
As DeusXM said the only way to know is to test, you might find you tolerate your cereal bar well (I wouldn't, cereal seems to make my blood sugar go bonkers). If you have a Holland and Barrett or independent health shop nearby it might be worth a look there for alternatives, they have a number of nut based bars that are lower carb. Be careful of oats they seem to be another divider food, I tolerate oats very well unless they're combined with hot milk (porridge essentially) but some folk find they don't work at all for them. I know it's a faff, but you could have fun testing different options.