I have quite the same problem. I want to install Manjaro Gnome 20.2.1 following this instruction:
However I get the same error as @wafelack. The installer doesn’t recognize the empty partition I created beforehand.
Considering the checklist you posted, @megavolt, I’d like to ask if the following warning, which I get when selecting AHCI instead of RAID ON in my BIOS, can be ignored:
“Changing this setting may prevent your OS from booting or require a reinstall …
The E-Module and other eSATA devices only function in AHCI or Raid On mode”
Also in my BIOS I can only set Fast Boot to “minimal” or “thorough” (I think thorough meaning a thorough = longer startup).