Some airways only go in one direction, like N872 in the north of spain that goes south. If you check that info in Skyvector that limitation is shown in the box arround the label (it represents and arrow pointing to the direction when only one is available and a box, no arrow, when both are available). When i check in Little Nav map it says in the manual that info is also displayed in the label of the airways (when there is only one direction) with a small arrow before the label. But I cannot see it anywhere. This is what it is shown in LNM. No arrow.

This entirely depends on the used simulator and if you have a Navigraph navdata update installed.

FSX, P3D and all MSFS simulators simply do not provide this information and lack even many more features like airway upper limits, MSA sectors, en-route holdings and whatnot. You have to update the sim *and* LNM using Navigraph to see this. There's nothing I can do about that.

Alex