Internal Website Optimization + SEO Improvement

According to SEO:
A semantic core is collected for the main sections of the site.
The title, description, keywords for the main page, as well as the main sections of the site for which it was formed.
The headlines of the H1 page for the main page are written and entered, as well as the main sections of the site for which it was formed.
Internal linking of the pages in the text content of the said pages.
Created the robots.txt file
Double pages and cyclic links are removed throughout the site.

According to programming:
Accelerated pagespeed to the green zone
The main mirror of the site.
Page with 404 errors
A self-generated map of the site
Created a self-generated XML site map
Created self-generated XML map of the site