While I don't know the details of what you're doing, I just grabbed the first hieroglyphics TTF font I could find and it seems to work as expected in a Godot label control. Here's the font I grabbed:
I added that to my godot project and then assigned it as the font for a
Label control. Adding some text to the label does indeed show the hieroglyphic characters.
One thing to be aware of. I assume that many (most?) such fonts won't contain a complete character set. That is, only some characters will convert to valid font glyphs. In my case, using the above font and upper and lowercase characters seems to work, but numbers don't (as the font doesn't contain the corresponding glyphs).
So, generally, it does work. How does the process outlined above differ from your attempts?