HighPoint should not even be installed within your system at this stage, unless you just want to use it as an external non-bootable drive.
Again, follow directions from this thread:
https://forums.macrumors.com/threads/mp5-1-what-you-have-to-do-to-upgrade-to-mojave.2142418/
Create a clean install of High Sierra on a spare SATA drive if you are still running into issues. If you do not have a spare SATA drive, would suggest you purchase one. Standard SATA SSDs can be found under $30 these days, or $50-75 for small capacity from reputable brands. It would make this entire process a lot easier.
Also of note, updating FIRMWARE does not change data on your drive. Launching an installer for High Sierra or Mojave to get a firmware update prompt does NOT install the OS unless you continue down that path. If you're that scared it will, CLONE YOUR DATA to an external drive. You should clone your data anyway, but that's another topic...