Spotlight wont search my hard drive

What I'm saying is that Catalina created the two partitions and if you wanted to revert to an old version of macOS, it's best to erase both those partitions first. You can do this by erasing the container disk.

Having done that, you can restart your Mac holding down Shift - Option (⌥) - Command (⌘) - R to boot into Internet Recovery mode. You don't need an external boot disk (although you can use it if you prefer).

This will install the version of macOS that your Mac initially came with and you can then upgrade it to any higher version of macOS that is compatible with your Mac.

Judekn wrote:

My issues started when i updated to macOS Catalina. My adobe software stopped working (crucial to my work) so I used a boot drive to revert to Mojave. In the process my hard drive split into two separate locations (Macintosh HD and Macintosh HD - Data). For clarity's sake, I'll refer to "Macintosh HD" as MacHD and "Macintosh HD - Data" as Data. All of my current information is stored in the Data drive.

The issue is that spotlight is only searching within the MacHD drive so none of my applications or files show up when I use spotlight to search for them. I have tried the usual solutions to re-index a drive. I have re-indexed the MacHD drive which changed nothing. I have also attempted to re-index the Data drive by adding it and then removing it from my privacy list (System preferences / Spotlight / Privacy) but i get an error upon attempting to add it into this list which blocks me from indexing this drive.

An annoying manual short-term solution I have found is to create an alias inside the indexed drive to allow for spotlight to find the file. I wrote that to provide a little help to anyone reading this struggling with the same problem looking for a quick "fix".

Any help is much appreciated.

How to rebuild the Spotlight index on your Mac - Apple Support

Mojave doesn't use the two partitions (MacHD and Data). That's something that Catalina uses. So if you want to revert to Mojave, you can erase the drive (Either the Container disk or the APPLE internal drive itself if it lets you) before installing Mojave and recovering your data. You may well then find you won't have the problems you're having because the drive has been appropriately partitioned.

Not sure if that helps you though; I hope it does.