What to do with such a redirect on the site?

Question

htaccess

The site is not mine (downloaded), but there is some garbage with it (
An error occurs here " https://www.dminterior24.ru/licensing.html " if you click on "Promotion 555"
+ how to remove .html at the end of the link

My .htaccess file:

Options +FollowSymLinks
RewriteEngine On

<IfModule mod_php5.c>

  # Устанавливаем кодировку UTF-8
  AddDefaultCharset	UTF-8

</IfModule>

<IfModule mod_php7.c>

  # Устанавливаем кодировку UTF-8
  AddDefaultCharset	UTF-8

</IfModule>

<IfModule mod_rewrite.c>

  # Убираем index.php на конце
  RewriteCond %{REQUEST_URI} ^(.*)/index\.php$
  RewriteRule ^(.*)index\.php$ https://%{HTTP_HOST}/$1 [R=301,L]

  # Убираем index.html на конце
  RewriteCond %{REQUEST_URI} ^(.*)/index\.html$
  RewriteRule ^(.*)index\.html$ https://%{HTTP_HOST}/$1 [R=301,L]

  # Страницы пользовательских ошибок
  ErrorDocument 404 /404.html

  # 301 Redirect
  Redirect 301 /akciya-555-m2	/akciya-555-m2.html
  Redirect 301 /work	/work.html
  Redirect 301 /studio	/studio.html
  Redirect 301 /licensing	/licensing.html
  Redirect 301 /index_1	/index_1.html
  Redirect 301 /index	/index.html
  Redirect 301 /contact	/contact.html
  Redirect 301 /confirm	/confirm.html
  Redirect 301 /akciya-555-m2	/akciya-555-m2.html
  Redirect 301 /SaveWeb2zip-order	/SaveWeb2zip-order.php
  Redirect 301 /404	/404.html

</IfModule>