My first question would be what type of soil are they planted in? Looks like wood shavings at least on top.

I can't see from your picture, but you should understand that the cotyledons, or seed leaves, which are the first ones to come out, don't last long. They usually start to dry up after the first true leaves emerge.

It's a potting soil mix from a store. It contains peatmos,perlite,humic acid,vermiculite,vegan compost.I use wood shavings as mulch @vgkg Z-7 Va

@daninthedirt (USDA 9a, HZ9, CentTX, Sunset z30, Cfa)I understand that but the leaves that die now are not cotyledons and I marked them in this picture with red circles

Assuming these are in a pot and you are growing in a warm climate, they are probably too wet. Do these get direct sun?

Yes they are in a pot but the weather is not warm/it is around 20 celsius during the day and around 13 celsius during the night/they get around 4 hours direct sunlight as the sky is cloudy and no rains/do you think it is a fungal infection?... @robert567

With only 4 hours of sun then the lower leaves may be fading out due to them being shaded by the upper leaves. If it spreads upward then the plant may have a fungal problem. The soil mix sounds ok, just be easy on the watering since a low light/heat situation won't dry them out very fast. Finger test the soil for moisture, it shouldn't need watering too often.