TTFB is so high!

I am using Digitalocean, 2 GB ram and 15 GB storage
My site has a very high TTFB, I am using Digitalocean from a long time and seen it is faster and really good but somehow the TTFB using cyberpanel is very high for my wordpress site.

I know that plugin, page size and other also affect it but I did remove all of the non-used plugin and made the page small.

What is wrong and what I should do?