What are the ways to speed up the site, except for the cache?

Question

CMS

I am currently working on a website. A site on a self-written CMS from one popular (but rudimentary) web studio. I am very dissatisfied with the website loading speed and server response time - 1.2sec.
There is some kind of cache in the xtacess, but what to do next? How else can you speed up the site? And please note that the point is not in its great weight, but in the speed of the server response and the speed of php scripts.

Answer 1

Maybe the technical component slows everything down ..
For example, the response time of the mysql server, etc. ..

Answer 2

Here, I wrote an article about it. Maybe you can take something here: archakov.im/post/kak-ne-stoit-izdevatsya-nad-saito...

Answer 3

Reactive Website Book
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https://gtmetrix.com
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checkgzipcompression.com
javascript-minifier.com
https://cssminifier.com
I think good hosting is the foundation of everything.
then caching everything, optimizing images and code,
gtmetrix will tell the rest.
All external .js are very slow