Hello.
Changing the max_input_vars values ​​did not solve my problem. I edited the htaccess file to fix this problem.
The value of the htaccess file was initially as

# BEGIN cPanel-generated php ini directives, do not edit
# Manual editing of this file may result in unexpected behavior.
# To make changes to this file, use the cPanel MultiPHP INI Editor (Home >> Software >> MultiPHP INI Editor)
# For more information, read our documentation (https://go.cpanel.net/EA4ModifyINI)
<IfModule php7_module>
   php_flag display_errors Off
   php_value max_execution_time 30
   php_value max_input_time 60
   php_value max_input_vars 300
   php_value memory_limit 512M
   php_value post_max_size 512M
   php_value session.gc_maxlifetime 1440
   php_value session.save_path "/var/cpanel/php/sessions/ea-php73"
   php_value upload_max_filesize 512M
   php_flag zlib.output_compression Off
</IfModule>
<IfModule lsapi_module>
   php_flag display_errors Off
   php_value max_execution_time 30
   php_value max_input_time 60
   php_value max_input_vars 300
   php_value memory_limit 512M
   php_value post_max_size 512M
   php_value session.gc_maxlifetime 1440
   php_value session.save_path "/var/cpanel/php/sessions/ea-php73"
   php_value upload_max_filesize 512M
   php_flag zlib.output_compression Off
</IfModule>
# END cPanel-generated php ini directives, do not edit
<IfModule mod_deflate.c>
    SetOutputFilter DEFLATE
    <IfModule mod_setenvif.c>
        # Netscape 4.x has some problems...
        BrowserMatch ^Mozilla/4 gzip-only-text/html

        # Netscape 4.06-4.08 have some more problems
        BrowserMatch ^Mozilla/4\.0[678] no-gzip

        # MSIE masquerades as Netscape, but it is fine
        # BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

        # NOTE: Due to a bug in mod_setenvif up to Apache 2.0.48
        # the above regex won't work. You can use the following
        # workaround to get the desired effect:
        BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html

        # Don't compress images
        SetEnvIfNoCase Request_URI .(?:gif|jpe?g|png)$ no-gzip dont-vary
    </IfModule>

    <IfModule mod_headers.c>
        # Make sure proxies don't deliver the wrong content
        Header append Vary User-Agent env=!dont-vary
    </IfModule>
</IfModule>

# BEGIN WordPress

 RewriteEngine On
 RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
 RewriteBase /
 RewriteRule ^index\.php$ - [L]
 RewriteCond %{REQUEST_FILENAME} !-f
 RewriteCond %{REQUEST_FILENAME} !-d
 RewriteRule . /index.php [L]

 # END WordPress

I used WordPress htaccess which is as follows and the problem was solved. I hope this change will not cause any problems