Problem installing W10 on 2010 iMac

[EffigyOfTheForgotten]

Hi, I've been struggling with this hard.

First off, I'm no expert, but with the help of Macrumors etc, i managed to upgrade my GPU & get Catalina working like a charm on my old iMac 2010. I also kept an install of High Sierra on a partition, just to have a backup. Next step is a Windows 10 installation, mainly to enjoy full Nvidia GPU driver support.

After tweaking with the info.plist file (took me many tries and way too long), I managed to create a bootable W10 64x usb drive (shows as "EFI Boot" when starting up with boot assistant). The iMac's superdrive is broken btw.

I then was able to re-partition the SSD with bootcamp, and that created the BOOTCAMP partition.

So, the current disk utility status:
Disk0: SSD (1TB, GUID Partition Table)
- Disk0s5: BOOTCAMP
- Disk1: Container Disk1 (100 GB, APFS-Container)
-- Disk1s1: High Sierra (APFS-Volume)
- Disk2: Container Disk2 ( 800 GB, APFS-Container)
-- Disk2s5: Catalina (APFS-Volume)
-- Disk2s1: SSD (APFS Volume, listed here for a second time for some reason)

Here is where the pain starts. Windows10 installer boots, I get to choose what partition to install to;

First off, I got the "GPT / NTFS" error, which I was able to solve using the gdisk tool, thanks to some other forum entries.

As expected, I'm shown 4 partitions (EFI Boot in the first place, and the other three partitions).
I select the one created for BOOTCAMP, delete it, create new -> Installer automatically adds two more smaller partitions (I read this is totally normal). I tried this in many different ways, formatted many times, repeated the entire process, etc.
The newly added or formatted parition is the only one allowing me to press "continue", always just to end up with this same error:

"we couldn't locate a partition or create a new one"

Whatever I tried over the past few weeks, led to this same error.

Can anyone tell what I could be doing wrong?

My suspicion is that it's simply not possible to run all three Os's from A GUID formatted SSD. Meaning I would have to re-format the whole SSD to MBR. But if that could be avoided, I'd be grateful, as I have a lot of beloved data and backing up & re-installing the whole thing would take ages.

Thanks in advance for taking the time!

 

[Going Bald]

This is a problem you should take to the Mac forums.

 

[EffigyOfTheForgotten]

Hi, just bumping this.

 

[trs96]

Hi, just bumping this.

Maybe the Bootcamp drivers you are using are too old for Win10. Can those be updated ?

 

[EffigyOfTheForgotten]

Maybe the Bootcamp drivers you are using are too old for Win10. Can those be updated ?

Hi, I don't think it's a bootcamp problem, as it lets me create the partition just fine.

After some research, I think the issue is that the partitions are not shown in the order which Windows10 is used to.

OR, like I said, maybe that the entire SSD should be formatted differently.

 

[jpz4085]

The newly added or formatted parition is the only one allowing me to press "continue", always just to end up with this same error:

"we couldn't locate a partition or create a new one"

Whatever I tried over the past few weeks, led to this same error.

Can anyone tell what I could be doing wrong?

I believe your old iMac would be installing and running Windows in legacy mode (hybrid GPT/MBR) unless there was an update or you're using some work around. It sounds like your USB installation media is UEFI from what you describe. Was the flash drive created by Boot Camp or some other method? If there are any other drives connected remove them if possible. If the flash drive has an EFI partition that could confuse the Windows installer too. FWIW that's my thoughts.