In some cases, the styles come from the theme CSS, which we can't modify. Use this code example to set the line height of the field label.

add_filter('frm_stripe_appearance_rules', 'adjust_line_height_label');
function adjust_line_height_label ( $rules ) {
    // Use 1 if you are using Twenty Twenty Three theme.
    // Use 22px if you are using Twenty Twenty Five theme.
	$rules['.Label']['lineHeight'] = 1;
	return $rules;
}