Many thanks!TWRP -> Andvance -> Terminal
if mmcblk0p8 is userdata partition, it had more space
# umount /dev/block/mmcblk0p8 (2 times)
Then back PC/latop:
# adb push /tmp/postmarketOS-export/acer-picasso.img /dev/block/mmcblk0p8
If it failed again, check your usb cable, i think 1.0 -> 2.0 support
Now I have another problem, when you start for the first time ubuntu mate 20.04 you have to configure, but when it is finishing it says the keyboard configuration fails and the configuration is cut off. Do you know why this can happen? could you connect the keyboard at the time of setting username and password? should I have connected it before?