Open MiFlash Tool, click , and point it to the ROM folder. Click Refresh to see your device.
Critical exploits like "BlueBorne" (Bluetooth) or "Broadpwn" (Wi-Fi chip) are only fixed via firmware-level patches, not just MIUI updates. Firmware Update on XIAOMI Redmi 5A
Yes, but only via Fastboot and only if anti-rollback (ARB) is not enabled. Redmi 5A has no ARB, so downgrading is safe. Open MiFlash Tool, click , and point it to the ROM folder