SOLVED:
I’m using intel mac, using the following steps in here.
wget https://dl.radxa.com/zero/images/loader/factory-loader.img
boot-g12.py factory-loader.img
then:
fastboot flashing unlock_critical
fastboot flashing unlock
for erasing bootloader, use this img (unplug and plug usb boot mode):
wget https://dl.radxa.com/zero/images/loader/rz-fastboot-loader.bin
boot-g12.py rz-fastboot-loader.bin
then:
fastboot erase bootloader
fastboot erase 0
fastboot erase 1
Using these steps i can erase the bootloader.