The main difference between "Extreact" and "General" (or "All Grain") is the Brewhouse Efficiency (BHE) field. It's not there in extract because whether high gravity or full volume boiled, it's expected that all of the wort, trub and all, will go into the fermenter.
Brewhouse Efficiency comes into play when some trub is left behind. BHE is simply the percentage of available sugars that make it into the fermenter. In OP's second example, the setting is General and the BHE is 72%. In fact, OP's boil parameters state 23.96 l, less 4% cooling and 0 l trub loss for 23 l batch size. That would indicate that 100% of the cooled wort went to the fermenter. So, OP's recipe likely told him that he needed more extract to get the gravity he targeted to make up for the loss.
The other issue that happens between the two settings is what BeerSmith does with any grain in the recipe. In General, BeerSmith will assume a higher amount of sugar from grain than in extract. When in General. the grain is assumed to be mashed, while in extract the assumption is steeping.
If you're not mashing, use "Extract" mode. That way, trub loss is simply a volume. Once you're mashing and leaving trub in the kettle, BHE becomes the best calculation to target gravity and yield.