Happyjack25 (or rather, Unhappyjack25),
I too recently purchased much the same retail version of MS Office for Mac2019 - at enormous expense I might add, reckoning that, once installed, it'd probably serve me well for around three years minimum. Previous editions of Office for Mac had. Don't know if yours is similar but with mine (the H & S version) you have to sign in to the MS account in order to manage it, and there's a setting for that on the Office menu bar at top of screen. I recall also that you have to look in your e-mail inbox for a confirmation message from Microsoft.
Initially, I had no problem in installing the app and then activating it. And incidentally, in the setup process for the installation I found on my copy (as with my previous edition) that I could select/deselect various of Office's components. I'm not sure if that's currently available also on your H & B version. That's to say, when I got to the Install caption of the Setup, instead of gayly clicking on Install I selected the Customise button. This gave all the app's components to choose for installing, including OneNote and OneDrive. I specifically didn't want those two, so I deselected them. The trick then was to click on 'Install', not 'Standard Install'.
However, I was utterly shocked to find that, after installing and activating, OneDrive was definitely running, and was actually copying every single personal/private file of mine from my entire system to the server! This was happening irrespective of whether I was signed in to the MS account or not. From the security angle, this was the very opposite of what I wanted to have happen, as I use secure offline methods for storing all my files. I was absolutely livid.
I logged in at the account and deleted what I could, then returned to investigate the OneDrive interface on my Mac in some detail. After nearly a day's work I concluded that there was simply no means of getting rid of OneDrive, it's compulsory it seems, so I decided to use Time Machine on my Mac to roll back to the pre-Office situation, getting rid of the Office account.
Since then, I've had another go at reinstalling Office, but this time the Microsoft server wouldn't accept my login password, even though it happily accepted the Product Key and my e-mail address. I tried again a day later but got the same result.
Mine was a 1 PC/Mac version (onetime purchase) and I've a suspicion that the Microsoft server won't (or cannot) respond to a second attempt at installation, even though the app may be already eliminated from the user computer. I gave up at that point, cursing Microsoft into eternity, and vowing to never use their products ever again. It rather looks like I've been swindled out of my money.
The revelation (if worthy calling it that) from you that my trouble may have been caused by their server being down is interesting, nonetheless. I have, however, embarked now on using LibreOffice instead, the free open-source office software. I've yet to actually install LO. But at least LO is pitched at serious users and not at the frivolous who accumulate short, inconsequential files where it doesn't matter if they get exposed/eventually hacked on a server somewhere.
MS Office was, for some decades, a stalwart applications suite that was IMHO well-designed but I'm afraid that in recent years Microsoft has dumbed down many of its features, seemingly preferrring to appeal to the less-serious office software user using mobile devices.