Bootcamp fail to install Windows 10 Pro on Big Sur 11.4

[dracir13]

Hi Everyone, thanks in advance. I'm posting this because I'm running out of solutions and I need serious help.

I've just recently bought last week a new 27"inc iMac 5k retina, 2020. It has macOS Big Sur 11.4 with this specs:
3,6GHz Intel Core i9 10n., 8GB 2667 MHz DDR4 RAM, AMD Radeon Pro 5700 XT 16GB and a 1TB os SSD Storage.

I want to install Windows 10 Pro using Bootcamp and giving a total of 370Gb into the Windows partition, which is enough. I'm also using the WINDOWS 10 21H1 ISO file downloaded from the Windows site.

I start Bootcamp, select ISO file, it downloads everything and restart the iMac. After restart, it appears Windows setup configuration and it begings to install passing all the ticks at the first installation window. After this, it needs a restart which gives you 10 seconds.... it restarts, appears for a few seconds the windows logo and the animation points below but it apparently crashes and stays in A BLACK SCREEN.

Nothing can be done, installation is stopped and the only way is manually stop iMac and even if you press option key to see different starting systems, there are 3. One for Machintosh HD and two for Windows. Clicking in none of the works.

I've called Apple support and they won't gave me any solution. I did what they told me: reinstall big sur and without any other installation previous to WIndows, it didn't work either.

I've also changed the security for my T2 chip to none security and able to boot from a usb external, but it didnt work.

What can I do? Please I need some serious help apparently.
Thanks a lot,

 

[pmiles]

Do you have FileVault turned on under Big Sur? Turn that off and then try again.

 

[dracir13]

Dear pmiles,
FileVault is off. That was another option that failed...
Thanks to you and all that are reading this post.

 

[dracir13]

Dear all,
I finally got it working!! I'll explain what I did in order to help other people Remember this is only for T2 iMac 2020.
https://support.apple.com/en-gb/HT201295

1) Reset the SMC.
Follow these instructions for Mac computers that have the Apple T2 Security Chip.

Mac desktop computers with the T2 chip​

Try this first:

1. Choose Apple menu > Shut Down and wait for your Mac to shut down.
2. Press and hold its power button for 10 seconds.
3. Release the power button, then wait a few seconds.
4. Press the power button again to turn on your Mac.

If that doesn’t resolve the issue, follow these steps:

1. Choose Apple menu > Shut Down and wait for your Mac to shut down.
2. Unplug the power cord.
3. Wait 15 seconds.
4. Plug the power cord back in.
5. Wait 5 seconds, then press the power button again to turn on your Mac.

2) Reset NVRAM
To reset your NVRAM, you use exactly the same procedure you once used to reset PRAM.

1. Shut down your Mac.
2. Press the power button, and as soon as you power up the laptop, hold down Command-Option-P-R.
3. Keep holding down those keys for about 20 seconds. Then let go and allow your Mac to continue starting normally. If you have an older Mac that chimes at boot, hold down the keys until you hear a second startup chime.
4. Then check the Startup Disk, Display, and Date & Time panes of SystemPreferences to make sure they’re set the way you want them.

I was told by the Apple Support Online chat to manually erase Big Sur 11.4 and to reinstall it after a COMAND+OPTION+SHIFT+R. Honestly I think by only doing the SMC, NVRAM and PRAM resets it would work. It's a fine line and dark line between macOS and Windows.
Please don't hesitate to reply if anyone is struggling with the same problem.
Thanks to everyone.
Salut!