If your injecting the secureinfo after the ctrtransfer your probably injecting the Korean secure info and causing the brick yourself, it may also be that the normal ctrtransfer is automatically injecting the original backup Korean secureinfo once it finishes and causing the issue, make 100% sure that the final secureinfo being used matches the ctrtransfer image you use, unless you make your own, afaik there is no publicly shared Korean one so your probably going to 9.2 US so you need a US secure info file, not a Korean one
I had followed ctrtransfer/region change guide that you mention several times. but still no luck.
Secureinfo_A is not important for now, because of this 2.1.0-4U condition I'm not insterested going back to korean firmware for moment.
I just wants to get a higher fimeware of USA region, not going back to korean region. So It just not related problem for now.
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To speck other people who read this, I'm not interested in for korean ctrtransfer or secureinfo_A for now.
and I don't think that could be a problem now either. (and doesn't wants to make this situation more headache)
So don't mention about korean region blur blur, It not a main problem.
(I already know that about 3ds system as well, that I already left in this article,
and I know that If the secure_info_A doesn't match with system nand title region, could be a brick or black screen that I know, so don't mention about that)
This a9lhed 2ds is just stuck on 2.1.0-4U (USA region) without nand backup, And I just wants to get a higher firmware (3.0~11.3) that same region (USA, not a KOREAN REGION).
And but somewhat weird, when I try to updated or ctrtransfered aren't working either (whatever I do - ctrtransfer, cartridge update, manual update; doesn't work)
THAT IS THE MAIN POINT.
So I left this article who someone interesting in this situation.
If anyone know about this or having same weird situation like me. Please share info with here.