What an unusual change, that once I did my best to keep the scfb driver uninstalled and now I have to use it. I recently upgraded my system from 14-stable to the newly available 15-stable. The usual process of updating src via git had a small hiccup due to a missing update to the blog post I perused. The minor detail I missed was that git switched to using https and that was what stopped the /usr/src update. All my blog posts now mention that git change where I had described the old method. The update was quick and building kernel and world went smoothly as expected.
When I was booted into the 15-stable kernel with world, I knew I had a lot of adjusting to do with regard to installed software or any other changes. I had saw an easy way to handle the task somewhere online. What I did was pkg upgrade -f right after I used gitup ports to update the ports tree. What I didn't know was that pkg was missing or not in a working state, so I had to do pkg bootstrap -f and after I did the pkg upgrade -f, I expected most things to just work.
You can make an educated guess that of course things did not work as expected or hoped. When I tried to start the X server so I could get back to using my pc as normal, it failed, some errors that seemed to be related to a mismatch with the kernel. I figured I could get past this issue by being certain to build locally with my updated ports tree. I rebuilt graphics/mesa-dri which pulled in graphics/libdrm (and I believe graphics/mesa-libs which makes sense), next I rebuilt graphics/drm-kmod which also provided gpu-firmware-kmod, after that was x11-drivers/xf86-video-amdgpu, next was x11-servers/xorg-server, and finally x11/xinit. I believed I had everything remade compatible with 15-stable and so I tried to start X again.
I must have assumed that I needed to reboot to have everything load properly, but this simply made me reboot a second time into single user so I could remove all the graphics stuff. Only after the graphics drivers were not trying to load could I boot into text only.
With all that I rebuilt, it gave an error that seemed to be a conflict between drivers? In the /var/log/Xorg.0.log file it seemed to load a raven driver and then picasso, but it couldn't find the amdgpu_picasso_gpu_info_bin file. No matter how many times I repeated the rebuild process to be sure I hadn't made any mistakes, I got the same result. The only way I could succeed to boot was to make sure the graphics was uninstalled, and usually I had to do that via single user.
With too many attempts already made, I remembered that there was the vesa driver which could work, and also the scfb driver I could try. I installed vesa first and tested it to see an unusable former 4k desktop squeezed into 640 x 480, everything huge on my 4k monitor. I didn't have mouse, so I couldn't exit fvwm or use an xterm to do anything, but I believe an alternate virtual tty was accessible, and I killed it from there. Next was the scfb driver which had always wanted to get in the way of the amdgpu driver in the past. When I got into X again, it was still quite large but much more usable. I also cured the mouse issue by building the mouse driver which was mysteriously missing.
I have during and since been searching for any recent reports or information about this issue. Most of the results are rather old, like 2019, or (of course) very Linux specific which does me no good, since their solutions are purely for that distro and its install methods. I did see mention somewhere about a change to driver naming or something, I am very unclear on that. That was in Linuxland, so if there was a change in that realm, we need to wait for it to be propagated into FreeBSD before maybe I will see a fix and get back to my amdgpu driver with 4k. I don't believe there is anything more I can do besides wait, but I will likely keep trying to get away from scfb.
UPDATE:
That was pleasantly fast. I suffered with graphics being broken and forced into second class scfb for my driver for only two or three days. Moments after posting the above, I went to /usr/local/etc/pkg/repos to edit the FreeBSD.conf file to disable FreeBSD-ports-kmods, and then upgraded pkg and updated, and after all the drivers were reinstalled, I have my 4k back. While I watched the update listing, it showed those graphics drivers did indeed all get updated to a more recent version. I cannot say whether there was a problem in the drivers or if any file was missing, or if strangely those kmod files were not pulled from FreeBSD-ports-kmods repo if that happened before. All that I can say right now is that my experience with the situation and my suffering scfb for a short time was documented above. How ever things got corrected, I am grateful for the work by those involved.