Clean up a joomla bloated website

I have a joomla websites with a lot of components in it. There is to much css and to much font's in the template (Rockettheme template) and then also a subtemplate from the stackideas templates.

I use JCH optimize but the site is still slow. Some big problems are this:

Reduce server response times (TTFB)

You can see here the pagespeed report
https://pagespeed.web.dev/report?url=https%3A%2F%2Fwww.glansbeton.be%2Fuitvoering%2Fbetonverharder

https://www.glansbeton.be/uitvoering/betonverharder