Please follow below instructions for the widget configuration on specific products.
Tag: show-donation-widget (Tag Name can be anything and you need to change it in the below code)
Add below code inside the product-template.liquid file:
{%- if product.tags contains 'show-donation-widget' -%}
{% render 'donation' %}
{%- else -%}
<!-- nothing to do -->
{%- endif -%}
Once you have added above code inside the product template you can assign the tag to the products on which you would like to have the widget displayed.