I exported 2 raster bands of Sentinel II (band 4 and band 8) to calculate NDVI (B8-B4)/(B8+B4), these 2 rasters are in EPSG:32630 - WGS 84 / UTM zone 30N. I'm currently using QGIS 3.26.1.
When I try to use raster calculator to do this NDVI my resluts are really bad, here are parameters I putted in : 
I'm supposed to have something that looks like what you can see on the left picture but I have what is on the right.
__________________desired result _____________________________________ result obtained