Display Content Based on Custom Field Value

You have a logical error.

You check if the field is != and not ==. So if the field name is Neutral the first check will fail and it will go to the second one and it will succeed.

You ask is Neutral not equal to Neutral and the answer is false because Neutral is equal to Neutral.

The same for the other ones.

<?php if( get_field('bias') == 'Neutral' )  { ?>
<img src="https://www.streetfiresite.com/wp-content/themes/streetfiresite/img/twoarrows-nuetral.png" />
<?php } elseif ( get_field('bias') == 'Bullish' ){ ?>
<img src="https://www.streetfiresite.com/wp-content/themes/streetfiresite/img/bullish.png" />
<?php } elseif ( get_field('bias') == 'Bearish' ){ ?>
<img src="https://www.streetfiresite.com/wp-content/themes/streetfiresite/img/bearish.png" />
<?php } else { ?>
<?php } ?>