How to use custom function in getAttr for page filtering

Site URL: https://dahlia-ellipse-3fcm.squarespace.com/

Hi there, 

I’m using Squarespace 7.1 to build my events website. We have 100+ events. I started to use the Portfolio Page templates because blogs and events templates are way too restrictive for what we need to display (the whole reason for moving to Squarespace was to have flexibility in our page templates).

I want to display all of my events on a page that has image blocks or a gallery view with the title (my preference is several image blocks that looks like a gallery). So users can then browse the events and select what they’re interested in. 

My issue is that the events run over 10 days across several categories - fashion events, talks, music events, etc. I want to add a custom filter so users can filter by both date and a category simultaneously. 
 

Is this possible? And if so, could someone provide an example of what a getAttr code should look like please? That would be amazing - I am not a coding expert but could take an example and make it my own (I think/hope).