I'm making a plant including power plants in a country. I plotted the plants and their symbology shows up in properties in the legend items but it does not in the legend itself as you can see in the picture below.
P.S.: Not sure if this is the reason why they might not show up but I used a different symbol size for different capacities as described in this other question: Categorising point layer twice by size and form in QGIS
How can I fix this so that the symbols of each plant are shown in the legend?