I can't make much sense out of what you have been doing. I can say that there is NO PROBLEM with dual boot between win 10 and ArcaOS, IF you get both set up properly.
Some quick, and dirty instructions, that should work if you adjust sizes etc. to match your hardware:
Okay, start over, and do it this way:
1) (This may not apply, in all cases) To eliminate some confusion, disconnect the SSD drive (unplug power and signal cables from the drive). We will worry about that after you get the rest working.
2) Use the disk utility, in the ArcaOS installer, to wipe the HDD. Boot the installer, and go to System Management-> Disk-> Disk utility. It will probably show errors (but may say "No problems found"). Ignore that, and click Disk-> Wipe disk information-> All disk information. After that finishes it will tell you to reboot. Now, you effectively have a new disk, with nothing on it.
3) Reboot, and go to System Management again. Run the Disk Utility again. This time, it will find that there is no partitioning (or something like that) on the drive, and it will offer to fix it. Fix it, and it will tell you to reboot again.
4) Reboot, and go to System Management. Go to Disk-> Manage Volumes (Graphical), and make ALL of the partitions. This is a 2TB disk, so I suggest:
250 GB (no less than 150 GB) for win. Select drive letter "none". Label it "Windows". Use a primary partition, and bootable.
20 GB for FAT32. Select drive letter D:. Label it "FAT32". Use a logical partition, and bootable. Don't make this too big, or it may cause problems.
4 GB for the OS/2 dump partition (not required, but why not?) I use drive letter N:. Label it "SADUMP". Use a logical partition, and bootable.
4 GB for your ArcaOS boot drive. Pick a drive letter (I usually use C:). add a descriptive label. Use a logical partition, and bootable.
500 GB for your ArcaOS data volume (or larger if you like). Pick a drive letter, and add a descriptive label. Use a logical partition, and bootable (Advanced is not useful, unless you have a small disk, and want to expand a volume to a second disk).
Since you probably want an alternate OS/2 boot system:
4 GB for alternate boot system. Pick a drive letter (I usually use Y:). Add a descriptive label, and select to put it at the end of free space. Use a logical partition, and bootable.
Fill the rest with another partition, to save the space. Use drive letter "none". Use a logical partition, and bootable (this will be removed later, and can be used for other things, as long as it is all done by LVM).
Save, then add Air Boot.
Save and Exit. You should be back at System Management.
Reboot (ArcaOS-> Shut down, then Ctrl-Alt-Del). It should go to Air Boot. It should show every drive that was installed as bootable. You can clean that up later.
At this point, you can try installing windows (probably best to disconnect the internet while you do this, and use win 10). It should install to the the first primary partition, without complaining, but don't forget to FORMAT the target partition, before starting the install (there will be an option, where you select the target partition). You may (probably will) need to re-install Air Boot after getting windows installed.
WARNING: win 10 (and probably other versions) will turn on a setting that cause windows to sleep, rather than shut down completely. This causes two problems: One is that it will leave disks dirty (probably only noticeable with FAT32 drives), and if you modify anything in OS/2, windows will "correct" the "problem" when it starts up again. Second, some BIOS implementations are told that they should use the "Fast startup" feature, which will override Air Boot, and simply start windows. To fix those problems:
In windows, there is also a power option to use sleep mode, when you shut down. In win 10 (8 is probably similar), go to Settings-> System-> Power & sleep-> Additional power settings-> Choose what the power buttons do (left side)-> Click on "Change settings that are currently unavailable", and turn OFF "Turn on fast startup".
TIP: When installing windows, it will offer to connect you to the internet. Tell it you don't have internet, and continue with limited setup. That will stop windows from trying to connect you to most of their garbage. You can connect to the internet later. Also, decline to help them, when it asks multiple times.
If that works, install ArcaOS to the volume at the end of the drive (Y:). The installer will format it (it should default to JFS) after you select all of the install options. That should just work, and Air Boot should recognize it.
Now, you should be able to use Air Boot to select which OS to boot.
If all of that works, format the rest of the ArcaOS drives (including FAT32, and format the SADUMP partition as FAT32, IF you have ArcaOS 5.0.5. or later), and proceed with installing your main ArcaOS system.
Now the advice! I have the bad idea to upgrade W10 to 2004 version.
Not true, but DO NOT try to update a machine, until windows offers the update. Apparently, some older machines will not be offered the 2004 update (and later versions, I would assume). Restoring a 2004 version, to a machine that isn't capable of running it, is sure to cause problems with windows. You will probably have activation issues too.