Is there a way to add a sidebar on the collections page that allows the user to click on the various product categories that are available?
After looking at it a bit, it seems like none of the free themes have this option?
Similar to how the sidebar is on this site
You can actually use Shopify search and discovery app to add collection based filters or you can add custom filters with the same app but using metafields. This is a free app and by Shopify.
Alternatively you can create this with custom code as well but search and discovery is kind of the go to option here.
Best
