Hi I hope somebody will see this soon, the case is hard to reproduce with a minimal example

I'm exporting a pdf using this command:

Export[NotebookDirectory[] <>
  StringJoin[StringRiffle[myParticleCenters], ".",
   StringRiffle[myParticleCutoffSizes, "-"], ".",
   StringRiffle[myHoleCenters, "-"], ".",
   StringRiffle[myHoleCutoffSizes, "-"], ".", ToString[c], ".",
   ToString[L], ".", ToString[\[CapitalNu]], ".t-",
   ToString@TimeUpperBound] <> ".pdf",
 Graphics[Inset[my3dp, Automatic, Automatic, Scaled[1]]],
 ImageResolution -> 220]

I can see a filestring appear when I run the command, but the file does not appear in the directory as shown

/Users/<...>/Mathematica/..10-101-191.1-\
1-4.10..201.201.t-100.pdf

But the file never makes it to the dir

I'm running macOS Catalina with no hope of downgrading to a sensical os

Never mind the operating system automatically hid the file for some reason

@1010011010 the double dots at the start of your file name are causing it to be hidden by default - it will also be hidden on a linux system at a plain old bash prompt; you'd need e.g. "ls -a" to see it, since dot and double dot are hidden by convention, so don't do that. I'd also recommend avoiding double-dots anywhere in a filename, just to avoid confusion.

however, for immediate use, if you open Finder in that directory, and tell it to show hidden files (Command + Shift + Dot), you should be able to see them.