I am working since 1 week to solve the TTFB time with around 2 seconds.
I have already minified CSS, JS and HTML. CDN also Images but doesnt matter. The Time is between 1.7 - 2 seconds.
TTFB is not going to be impacted by your CSS, JS, Images or the size of your HTML. It is just about entirely the server processing time to generate the page. You need to look at your application on the server and/or your hosting to solve it.