How I can clear the fusion drive from all rest of earlier Bootcamp Installation

I have it!

I run sudo diskutil mount /dev disk1s1

I find in Finder EFI 😉

In EFI i have found 3: APPLE BOOT WINDOWS

I delete Windows.

I boot with ALT and found windows gone but EFI BOOT was there as a boot volume!?

So I make again steps to the EFI and delete the BOOT

Now everything is fine!!!!

Thx Loner T for your help.

So Apple Support could not help me....but YOU can 😉

Here Output from diskutil list:

Manfreds-iMac:~ manne$ diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *121.3 GB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_APFS Container disk2 121.1 GB disk0s2

/dev/disk1 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *3.0 TB disk1

1: EFI EFI 209.7 MB disk1s1

2: Apple_APFS Container disk2 3.0 TB disk1s2

/dev/disk2 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +3.1 TB disk2

Physical Stores disk0s2, disk1s2

1: APFS Volume IMac HD 1.1 TB disk2s1

2: APFS Volume Preboot 45.8 MB disk2s2

3: APFS Volume Recovery 512.8 MB disk2s3

4: APFS Volume VM 2.1 GB disk2s4

/dev/disk3 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *3.0 TB disk3

1: EFI EFI 209.7 MB disk3s1

2: Apple_HFS My Book for Mac 3.0 TB disk3s2

Manfreds-iMac:~ manne$

No I have nothing changed on File and Partition System of the Macs Hard drive before Mojave. After Mojave and boot into Windows (here everything was fine) and later boot in MacOS via ALT Key booting was so slow...you can drink three coffees in that time. So something was wrong and I could not change this. So I force a clean installation via Recovery. I do not recover a Time Machine Backup, I do everything new. But boot via ALT WindowsVolume is there?????? I do not know what mechanism this is? There is a rest of Windows there...where it is? When boot via ALT...from where come this information? Where is this Windows Volume?

Ok, that helps a little bit. Which one? And...how I can find it out which one? When I boot now in Windows a repair display is there but nothing could repaired. So there is a rest of this Win10....where? Is it possible to check? Is it VM and RECOVERY? Or maybe it is an invisible partition?

Ahhh sorry for my English.

No, sorry it was my fault. I upgrade without delete of BC Partition. If I boot wit ALT, I see a Windows BootVolume, If I look in StartupVolume, there is only MacOS.

Could not mount the disks

Yes, it is mounted...so how I can check?