I am the original owner of a mid-2012 MacBook Pro, which is currently running 10.14.6. On it I am running VMware Fusion 11.5.5. I created a VM of OSX 10.11 El Capitan so I could help a relative who uses it.
I do not want to use my personal iCloud account on this VM so I created a new Apple account, validated it, and it now works on a spare iPad. Let's call it my "Test Apple Account".
When the 10.11 installation on the VM reached the point where it asked for Apple Credentials to set up iCloud, et al, I enter the Test Apple Account ID and password, received an approval request on the spare iPad, allowed it, entered the 6-digit code, things were looking good, and then the following dialog box appeared.
I entered the password I always use to sign into this MacBook Pro and after several seconds red text appeared in this dialog box saying it's the wrong password. I tried a couple more times thinking I was misspelling it and now that account is supposedly locked for 24 hours.
I've seen a few forum posts on the Interwebs about this issue but they all veer off on sidetracks, including one on the SuperUser forum. My application is about as clear cut and legal as it gets.
BTW, as a test I used the same Test Apple Account for setting up iCloud in another User account on this MacBook Pro. It worked fine. So what's different about this attempt to sign in to iCloud is that it's on an OSX 10.11 VM in Fusion stead of a 10.14 meatspace MacBook Pro.
Hmm. I wonder if I should be running the VM from that account? I'll check that and report back.