Try to find this miflash tool: MiFlash2018-5-28-0, go into fastboot, connect and then it should work with this fastboot rom: sirius_images_8.10.25_20181025.0000.00_8.1_cn. Extract it to a .tgz-file and than flash. Otherwise I don't know.
The MiFlash tool cant detect the phone, i dont know why. My Mi 8SE is only able to show the fastboot screen and the only thing that works is that in the cmd i can see the device when i type fastboot devices