Boot Camp install issues on late-2013 iMac 27", replaced HDD with SSD
I have a late-2013 27" iMac that previously had a 3 TB Fusion Drive, which ran for several years with Boot Camp until the HDD started failing. I have replaced the HDD with a 2 TB SSD, running alongside the original 128 GB SSD blade. They are separate volumes (I didn't re-FUSION them).
I am trying to install Windows via Boot Camp assistant on the 2 TB drive. I have created the USB install stick, using the Win10_1903 (May 2019 Windows release), which I've verified that I can boot from by holding down the option-key. When I ask Boot Camp to only "Install or remove Windows 10 or later version," it downloads the Windows support software and then returns to the internal disk selection screen without partitioning the drive or reporting any error.
I have also tried using Disk Utility and skipping Boot Camp. The Windows installer won't proceed past formatting the partition (I haven't tried reformatting the whole disk, since my primary MacOS user directory is on this larger drive).
Beyond that, I have:
Reset NVRAM
Reset SMC
Deleted local TM snapshots via tmutil
Tried installing on the 128 GB blade instead (both via Boot Camp and not)
My next best guesses are to create another Fusion drive of a single volume and restore the user data from time machine, or try something clever with a virtual machine -> external HDD -> cloning back -> pulling my hair out.
Anyone have any better ideas? Or guesses as to why Boot Camp is failing with no error feedback?
Here is the output of "diskutil list (disk4 is the USB stick)"
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *121.3 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_APFS Container disk3 121.1 GB disk0s2
/dev/disk1 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *2.0 TB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_APFS Container disk2 2.0 TB disk1s2
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +2.0 TB disk2
Physical Store disk1s2
1: APFS Volume Lazarus 191.6 GB disk2s1
/dev/disk3 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +121.1 GB disk3
Physical Store disk0s2
1: APFS Volume Commander 17.4 GB disk3s1
2: APFS Volume Preboot 45.7 MB disk3s2
3: APFS Volume Recovery 509.7 MB disk3s3
4: APFS Volume VM 2.1 GB disk3s4
/dev/disk4 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *62.6 GB disk4
1: DOS_FAT_32 STALL 62.6 GB disk4s1
iMac 27", macOS 10.14