In tpl_checkout_payment_default.php, I can see the logic for building a bootstrap-style checkbox for payment methods that have a field which includes a checkbox - it's on line 120 in version 3.7.0.

But this doesn't seem to fire correctly for Authorize AIM, which does

$selection['fields'][] = [
'title' => 'Keep Card on File',
'field' => zen_draw_checkbox_field('authorizenet_cim_save', '', true, 'id="authorizenet_cim_save" '),
'tag' => $this->code . '_save',
];

and produces

<label for="authorizenet_cim_save" class="inputLabelPayment">Keep Card on File</label>
<input type="checkbox" name="authorizenet_cim_save" checked="checked" id="authorizenet_cim_save" class="custom-control-input">

which is lacking the enclosing div of class "custom-control custom-checkbox" (and thus does not actually display a checkbox, just the text.)