That support is only for paying Relevanssi Premium customers. Relevanssi support is here. (I’m not sure which one is this about; Premium is mentioned, but 4.1.2 is not a Premium version number.) However, tagging posts with relevanssi
does summon me, so this works as well.
Anyway. I’m not sure I fully understand the question. What exactly are you looking for to happen here? Which of these options are you looking for regarding the product categories?
A) When you search for a product category, the search will return all products in that category.
B) When you search for a product category, the search will return the product category archive.
The option A is possible with free Relevanssi (which you seem to be running if you have Relevanssi 4.1.2), it’s just a question of making Relevanssi index the product category taxonomy. Any ACF fields in the product category terms won’t have any effect on anything.
The option B requires Relevanssi Premium (current version of which is 2.2.5). In this case, it’s possible to have Relevanssi index the ACF fields for the categories. In this option, you’re pretty much guaranteed to run into problems with your theme, because WooCommerce themes generally only like to show products, and the search layouts often break down if you want to include something else.
If you’re looking for option A, please post a thread on the Relevanssi support forums, describing the issue in more detail. If you’re looking for option B, make sure your client has a valid license and then use the Relevanssi Premium support form to send me a support request with more detail in it.
The second tutorial you mention is not related to the topic in either case. In any case, you rarely want to index ALL custom fields; VISIBLE is almost always the better option, especially with ACF.