Ok, I now found the image function on the left side of the Core in UIFlow.
I was looking for it in the regular list of blocks, especially in "Graphic".
from m5stack import *
from m5stack_ui import *
screen = M5Screen()
image0 = M5Img("/sd/images/sled150.png", x=0, y=0, parent=None)
It would be great if it could also show JPG files, they still seem to be more common.
Note that lcd.image() can display JPG files, but it crashes loading from micro SD card.