I found a solution to this which is flashing the stock ROM using the adb/fastboot tools, but I used an older version because the latest one didn't work for some reason and I followed the guide on google's website hope that'll help someone. :)
If your rom developer does it you can just
fastboot update rom.zip
Where rom.zip contains android-info.txt and at least boot, system, product, vendor, vbmeta, and dtbo img files.
If necessary unzip and rezip creating an empty android-info.txt.
Img files contain an exact replica of the partition which is copied exactly onto the device
I own a OnePlus 7 and the same developer has answered a similar question in One Plus 7 device forums
I just noticed, the script in bat file only flashes 25 .img files, but when I extracted payload.bin in OB2 I saw 32 .img files. Does this mean that the other .img files in payload are not needed? Or can I add the command in bat file to flash ...
Something like a secondary bootloader. Is that possible?
Yes it's possible. As you mentioned, since the boot chain up to bootloader stage is closed source and binaries are signed with OEM's private keys, it's not possible to replace or modify the bootloader. However if bootloader is unlockable, it's possible to boot a custom kernel (your own OS). But the ...
You need to set ANDROID_PRODUCT_OUT in /etc/environment.
You may have a folder with boot.img and system.img etc. in, this is the right folder.
After that you can call sudo fastboot flashall -w
It also works for self builds.
So what worked for me was to flash it, let it fail, extract the rom file (tar.md5) flash the system.img and then the hidden.img after the first. Reboot in safe mode (volume up + home button + power) and boot from /system
yes, TWRP is built OS-version specific
the reason is changes in android versions may differ in
file system type
most (if not all) updates are backwards compatible. that means the TWRP is ready for android 9 but you can still run android 8 on your device
Caution: I have rooted my device for the first time, I have no prior experience in rooting. Continue at your own risk.
I am not sure about the RAM part, but we can flash the custom ROM from the internal SD card too. The following link is for explains the installation process for Installing CM 10.1 on Galaxy Tab2, however, we can follow the same steps for GT-...
Alecxs helped me with the solution so I am posting the solution that worked for me.
Install MIUI 184.108.40.206 fastboot ROM (it works with this only) and extract it to C drive.
Run MI flash tool and select the extracted folder.
Now boot the phone to EDL Mode and immediately click refresh and then click flash.
Because if you are even 2-3 seconds late then process ...