"Where=" in template?

First of all Hello to all,

I am new to the community and just a hobby developper. Something I am sure pretty simple has been bugging me for the last days and I will try to explain my issue through a simple example.

Lets consider an online forum where I have Categories of Forums and in each of them one of more forums.

I would like the final result in my template to be something like:

{{#each category}}
{{#each forum where forum.category=category}}

and that would list the category and for each of them the different forum inside of it.

My questions are:
would be what’s the best approach for such a problem ? meaning:
Shall forums be a sub-elements of the categories in the Schema but then the shcema seems a bit complicated.
Shall forum and categories be separated schema but in the same collection but then how can I do this “where” in the template ?
Do I have a totally silly approach on the issue and I missed something in the tutorial ?

Thank you in advance for your reply.