I went through the same frustration with the activation. I downloaded the entire suite to see if anything worked. Oddly, the Onenote app did. I found that strange but didn't think too much about it.
I called Apple support, who couldn't figure out why I couldn't activate, transferred me to technical support, to see if I could return to the 32 bit OS. I was told to contact Microsoft before I called back. While I was waiting for Microsoft to call I fumbled through some of their troubleshooting and came across this, regarding Ipad: https://support.office.com/en-us/article/-no-subscription-error-or-problem-signing-into-office-for-ipad-using-an-office-365-organization-id-account-1ceccc05-6954-4fac-b12d-e54341ad898e?ui=en-US&rs=en-US&ad=US
Apparently, on an Ipad I lost a year ago, Onenote (or maybe an Office version) was preinstalled. It was still associated with my AppleID. When I lost it, I locked it, but did not erase the Ipad or delete it from my account in the hope it would be found. I went into my Find My app, erased the IPad and then deleted it from my account. Opened up one of the apps in the MS Office 365 Suite, clicked "activate" and oh my goodness after two days of trying to install, reinstall, delete accounts, change payment options, cancel subscription, rebuy subscription, sign into Microsoft.com, etc, it worked like magic.
I am appalled the good folks at Apple support did not ask me if I had devices that may have had a previous version installed. I am even more appalled that ten hours later, I am still waiting for a call from Microsoft.
I hope this helps someone as it has stressed me out for two days. And it wasn't even on my computer but on my husband's, who is an attorney and who was batty that he lost all his docs.