For Android 10
You have to copy the rockdev/Image* folder to RKTools/linux/Linux_Pack_Firmware and rename it to Image.
Then run mkupdate_rk3399.sh.
Use the generated update.img here and not the one in the Image folder.
You can create the following file in the root directory.
vim ./pack_image.sh
#!/bin/bash
PROJECT_PATH=`pwd`
cd RKTools/linux/Linux_Pack_Firmware/rockdev/
./mkupdate_rk3399.sh
cd $PROJECT_PATH
mv RKTools/linux/Linux_Pack_Firmware/rockdev/update.img .