I don't know if this insight will help anyone, but I checked my three machines that have Office 2019 on them. Installer from each came from MS Guides. Maybe links on the site, but definitely MS Guides.
One has Version 2008, Build 13127.21624 Click to Run on it, installed early 2020 I think. Never had a problem with this one.
Another has Version 2104, Build 13929.20386 Click to Run on it, guessing installed in March of this year. Seems to never have had a problem; this replaced an Office 2016 version that started giving the "there's a problem" message.
The computer I'm on at the moment also has Version 2104, Build 13929.20386 Click to Run, installed a week ago after the Office 2016 version I had started giving the problem message.
The conclusions I draw are that the Version 2008 somehow isn't affected by this. I may still have the installer on that computer. But the Version 2104 does somehow generate the error message. But I can't figure out why the 2-3 month old version never generated the error, while the newer one did in a matter of a few days.
The only other material observation I have is that from the file > account information, the 2008 and the newer 2104 just show "Product Activated" under "Office." Whereas the older 2104 has a clickable "show additional licensing information" under "Office" - when clicked, it says the product is activated. My guess is the machine has inactive license keys on it.
Insight, anyone, from the above?