Trato de instalar la antigua versión (android 9 descargada de la pagina oficial) y sale esto:
fastboot flash a C:\ROM\images\system.img
target reported max download size of 534773760 bytes
sending sparse 'a' (522236 KB)...
OKAY [ 20.619s]
writing 'a'...
FAILED (remote: Partition flashing is not allowed)
finished. total time: 20.719s