Product Filters

For filtering products, you can add tags to the products so these are then displayed in the filter drop-down.

This can be enabled in your theme's settings:

1. Admin

2. Online store → themes → customise

3. Collection pages

4. "Enable filter"

Shopify Help - Using Tags guide​

Apps:

Here are some apps which may be a good fit, as an alternative: Product Filter Search - Shopify apps Power Tools Filter Menu - Shopify apps Udundi Filtering - Shopify apps Collection Filter - Shopify Apps Smart Product Filter - Shopify apps​