Hopefully this specific situation is unique and will not repeat itself. I mean it's kind of awkward seeing such an issue with a FreeBSD Release. Consistency is one of the points that made me come over from the Linux world.
I have been hit by the very same problem during my first current FreeBSD installation on my laptop, not knowing about it because not having looked at the errata or mailing list (of course my bad, these are things I just have to get used to).
12.0R will be EOL at the beginning of February 2020, so another month to go with building graphics/drm-fbsd12.0-kmod from ports, which was no problem at all and immediately fixed the issue.
obsigna nice upgrade script btw! I really have to get into scripting again.
I wonder how many brave souls FreeBSD is putting off at the moment. It literally ships with broken "GUI experience" for multiple months. I, honestly, don't understand this decision to wait until the EOL of 12.0. Sometimes we boast about it being a very dependable and reliable system, sometimes we prefer to pretend FreeBSD has nothing to do with the ports collection, or, at least, it may appear so to the newcomers.