TextMesh Pro & OS Font

Use the following instead.

// Get paths to OS Fonts
string[] fontPaths = Font.GetPathsToOSFonts();

// Create new font object from one of those paths
Font osFont = new Font(fontPaths[index]);

// Create new dynamic font asset
TMP_FontAsset fontAsset = TMP_FontAsset.CreateFontAsset(osFont);