import arcpy
import os

#nearly 700 rows of script

fclist: [ ...] # some fc
rasterlist = [...] # many raster
for raster in rasterlist:
    rasterpro = arcpy.ProjectRaster_management(raster, "in_memory\rasterpro", 25832)
    for fc in fclist:
        os.makedirs(newfolder + "\" + filenamenew + "_" + os.path.basename(fc))
        arcpy.SplitRaster_management(rasterpro,
                                    newfolder + "\" + filenamenew + "_" + os.path.basename(fc), # it is a correct path, which should work fine
                                    filenamenew + "_" + os.path.basename(fc) + "_",
                                    "POLYGON_FEATURES",
                                    "#",
                                    "NEAREST",
                                    "#",
                                    "#",
                                    "#",
                                    "#",
                                    "#",
                                    "#",
                                    fc)

# some more rows of script