Instead of using that character for your arrow, you could use a different character and wrap it in the FNT formatting tag specifying a symbol font. For example, the ESRI Business font includes some bold arrows that could be useful.
"<FNT name='ESRI Business'>a</FNT>" produces a right-facing arrow
"<FNT name='ESRI Business'>b</FNT>" produces a left-facing arrow
If the character is embedded in your attribute table instead of in the label expression, use the Arcade Replace function to replace the characters → and ← with the above formatting tags.
