Should I need remove the .html or .php from my URLs for improving SEO?

The answer is NO.

Google is not caring about the extension of page URLs like .php or .html.

Google bots treat URLs the same, even if it does not contain the extension or also if it includes many query parameters.

In many cases, Google bots will consider the same URL with different query parameters as a separate page.

But this has no direct effect with the .html or .php extension of page URLs. Google bots treat them all the same.

You will not have any benefit in adding or removing the .html or .php from URLs.

What you need to do if you remove .html or .php

Removing these extensions means you are simply rewriting the URL structure for a better or cleaner URL.

So you may need to do the following:

1. Carefully use .htaccess or Nginx to rewrite the URLs to prettier ones...
2. Use a 301 redirect to the cleaner URL from the older ones. So all the ranking benefits of the original URL will be carried to the cleaner URL.

How about user experience?

In terms of user experience, it will have a positive effect. Visitors always prefer a clean URL even without any query parameters.

When users go to a page on Desktop, there is more chance they may look at the URL structure. You have more chance of user to share your content on social media with a descriptive URL.

Wrapping Up

There is no direct effect on SEO if you use it with .html or .php on the end of URLs. But make sure you are not confusing users by showing two pages at the same time.

Make sure to redirect with a 301 status code of the pages end with .html or .php to clean URLs.