Best SEO Practice for URLs

I'm looking for some clarity on best SEO practice when it comes to URLs.

First, should I be using www or not? For example, is it better to go with:

https://ipop.co.nz/
or
https://www.ipop.co.nz/

Also, I read on an SEO forum recently that product URLs should drop the .html at the end. So instead of:

https://ipop.co.nz/mens-sunglasses-nz/p ... chief.html
it would be:
https://ipop.co.nz/mens-sunglasses-nz/pz2011-blk-chief

Do these changes actually make a difference for SEO, or is it more about user preference and having cleaner URLs? Thanks

1. www vs. non-www Domains

Google treats https://ipop.co.nz/ and https://www.ipop.co.nz/ as separate URLs. To avoid duplicate content issues:
Choose a preferred version (either with or without www).
Implement 301 redirects from the non-preferred to the preferred version.

Set your preferred domain in Google Search Console.
This ensures consistency in indexing and consolidates link signals
https://developers.google.com/search/bl ... red-domain

2. Use of .html in URLs

Google recommends using clean and descriptive URLs without unnecessary file extensions like .html. For example:
Preferred: https://ipop.co.nz/mens-sunglasses-nz/pz2011-blk-chief
Less Preferred: https://ipop.co.nz/mens-sunglasses-nz/p ... chief.html

Clean URLs enhance readability and user experience.
https://developers.google.com/search/do ... erce-sites