The "MT" in stands for Monotype. This is a critical distinction. Monotype is the foundry that owns and licenses Arial. When you see "MT" in a font menu or file name, it refers to the specific version of the font sourced from the Monotype library. This is often considered the "original" and most stable version of the font, distinct from variations that might have been cloned or adapted by other software vendors.
Do not expect Arial MT Black to suddenly look like a saloon sign. You need a dedicated Western font. Arial Mt Black-black -western- Free Download
Once you’ve found a “Black Western” font (like The Black Western or Blazing), here is how to install it on your system. The "MT" in stands for Monotype