How can I get all entries that are equal to, but not after a date?
I think the only issue is that you're adding "today" to the query as a string, not the variable you've created. try:

{% set today = now %}
{% set events = craft.commerce.products.type('event').eventEndDate('&gt;=' ~ today) %}


The code in the answer you referred to had the same error, I've fixed it.