Did you post the correct link for your first question? That thread isn’t specifically about external files and nothing in it sounds like a non-Obsidian workaround.
I haven’t linked to any files outside of Obsidian yet, but when I do, I plan to put a unique ID in the name of every file I want to reference, and never change that part of the name. It’s not pretty, but unfortunately I can’t rely on files having the same path on my home computer and on mobile devices. If the link doesn’t work, then searching the ID number in the file manager should find the file.