I see this line listed in the Microsoft 365 Business FAQ on the main MS website
"*Windows 10 Pro upgrade rights are included with the Microsoft 365 Business preview if the target machines are presently running Windows 7, 8, or 8.1."
I take it now M365 Business is out of preview this is no longer the case? Could we get this text removed from the website so not to confuse any end users?
Its a shame this wasn't included in the final product as lots of SMBs have machines with home versions of Windows installed with no cost effective way to upgrade them other than wait until the machine is due for replacement.
The message I've always seen and had drilled in to me that this was a 7/8.x Pro to 10 Pro upgrade, and that it specifically was not a Home to Pro upgrade. I've pasted the text from an older version of the FAQ pdf, which gives some additional context because the asterisk in your post might have referred back to something which was a bit clearer. I went back through the docs article history on GitHub and only saw references that do support Pro to Pro.
There was definitely some confusion about what the Pro/Business upgrade was or what it included, so you aren't alone in your thoughts.
Customers that wish to experience the complete capabilities of Microsoft 365 Business must be running Windows 7, 8.1 or 10 Pro* on their existing desktops. Customers who use on-premises Active Directory must switch to cloud identity and management as part of their deployment. Existing Windows 10 Pro PCs should be running Creators Update if they have not already done so.
*Devices running Windows 7 or 8.1 Pro are eligible for an upgrade to Windows 10 Pro within the Microsoft 365 Business preview.