How does the filter mechanisms in e commerce websites like Myntra, Amazon, Flipkart, etc., work?

Example 1: Take a website like Myntra (use this URL for reference -> https://www.myntra.com/men-tshirts?f=Categories%3ATshirts ). Here we have 21 filters for selecting a t-shirt. And everything is optional. What way of coding is required to achieve this ? Do we need any sort of design pattern or how are the permutations of all these handled in the backend.

Example 2: Consuming a Swagger API with multiple filters. Ideally you've to hit the URL (or construct the URL) based on the filter parameters you want. This again is similar to the above one of building a URL based on optional filter conditions.

Can someone provide insights on the approaches used or the best practices to achieve such tasks? I use Python and Flask, so anything in that line would be extremely helpful. If not, concept alone would be of great help.