Installing TWRP recovery on Redmi 8A isn't an easy task because of its Partition Scheme. There are two types of partitions, A/B partitions and legacy A-only. Both have different types of methods to install TWRP on it.
You can use Treble Info App to find out your device's partition type. Or check it by running the following command in ADB shell or a Terminal Emulator app:
getprop ro.build.ab_update
This will return “true” if the device supports A/B partitions. On legacy A-only devices, the output should be blank.
Before we proceed with the installation of TWRP first we need to unlock the bootloader. Some companies provide a specific tool to unlock the bootloader. But it can be done using command line tools too. You can check this source to know about it or search with your device name and model name to find out how to unlock the bootloader on your device.
Case I: Devices with A-only partition scheme
If your device uses the A-only partition scheme, then you can directly replace the stock recovery image with TWRP via Fastboot.
1. Download And Copy the twrp image to a suitable location.
2. From your PC, open a command prompt/terminal and type:
--> adb reboot bootloader
3. Rename the TWRP image to twrp.img and type:
--> fastboot flash recovery path/name.img
where path represents the path and name is the actual name of twrp file
--> fastboot reboot
1. Many devices will replace a custom recovery automatically
during first boot. To prevent this, search to find the proper key combo
for your device to enter recovery. After typing ‘fastboot reboot’, hold
the key combo and boot to TWRP.
2. You can also try to temporary boot the downloaded image using the following command:
--> fastboot boot twrp.img
3. Once TWRP is booted, TWRP will patch the stock ROM to prevent
it from replacing TWRP. If you don’t follow this step, you will have to
repeat the installation.
4. Congrats! TWRP is now successfully installed on your device.
Case II: Devices with A/B partition scheme
With devices having A/B partition scheme, the recovery and boot image
both are merged. Due to which, you need to temporarily boot TWRP first
and then perform the permanent installation within the recovery
1. Copy the TWRP image to a suitable location on your PC. You can
even put it on the folder where the Fastboot binary is located.
2. Download And Copy the twrp image to a suitable location.
3. From your PC, open a command prompt/terminal and type:
--> adb reboot bootloader
4. To boot with twrp enter:
--> fastboot boot name.img
5. Copy the twrp.img file to the device by using mtp or Enter:
--> adb push name.img /sdcard
6. Navigate to the Advanced menu of TWRP and tap on “Install Recovery Ramdisk”
7. Install recovery ramdisk option under TWRP
8. Choose the twrp.img file from the device’s internal storage.
9. Swipe to install and then reboot.
- TWRP is Now Successfully Installed On your Device
More on this topic can be found here