There are certain recommendations from Google Page Insight Speed reports that are not possible to be handled from code (and this applies to any website that offers you services like Google Maps, IDX support, and so on).
Also, consider that you have plugins that each come with their own js/ CSS files.
Minify is a process that basically encodes files. Theme files can be minified from Theme Options > Advanced > Site Speed
External resources about minifying –https://developers.google.com/speed/docs/insights/MinifyResources
Enable caching for third party – Google Maps – is not possible because Google doesn’t allow it.
Optimize images is something each person does as images are added by each client.
On items like Remove query strings from static resources- there’s nothing to do since the variable detected in the script version from wp. And it will gain no actual speed.
For the server you have 2 important things you can do:
- Specify a Vary: Accept-Encoding header
- Enable gzip compression
If you are using 2 types of URL – with www and without www – Use only the one with www.
Use a cache plugin like WP Rocket – besides cache, it also does minify js and CSS.