My report from upgrading a mid-2011 iMac 27" with AMD Radeon 6790 GPU:
- As has already been stated in this thread, the Disk Utility included in the Mojave Patch tool can't mount encrypted APFS volumes. It never asks for a password and doesn't mount the drive. It doesn't work via command line either (diskutil mount). It is therefore necessary to disable Filevault before installing Mojave, and re-enabling it after. I don't think this issue is confined to the mid-2011 iMac.
- Without the Legacy Video Patch, the system operates without graphical glitches in dark mode. However, it doesn't detect my external monitor. With the Legacy Video Patch installed, it detects my monitor but it has the issue that has already been reported of the window contents not refreshing when dragging a window.
- The video performance is jerky (not smooth) even for everyday operations like scrolling Web pages in Safari, the animation when opening folders, etc. This is of course due to the lack of video acceleration.
I went into this with my eyes open, fully aware of the limitations of running Mojave on this model iMac. I wanted to see for myself. My conclusion is that the tradeoffs are unacceptable (for me at least) and I'll be reverting to High Sierra.
By the way, nice touch to the Mojave Patch Tool: a "Restore System from Time Machine Backup" utility is now included (it wasn't present in the High Sierra Patch Tool). This makes full system recovery quite easy, assuming one has a valid Time Machine backup of course.
Thanks to dosdude1 for providing the patch tool! Unfortunately, High Sierra seems to be the end of the line for this old iMac. Time to upgrade...
-cinergi