MS has a history of fucking up LibreOffice installs.

https://wiki.documentfoundation.org/Faq/General/General_Inst...

I am sure this is by accident, MS would never try to discourage users from installing free alternatives to their offerings.

Perhaps this from last year, though it doesn't directly involve code-signing: https://www.neowin.net/news/microsoft-bans-libreoffice-devel...

Maybe this from 8 months ago?

https://news.ycombinator.com/item?id=44728369