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Absolutely not!

God forbid if adding security to your site required you to start from scratch. That would be nonsensical.

Most likely, your existing site's configuration.php file has a non-blank $live_site line. That line must read:

public $live_site = '';

Nothing between the two single quotes.

Okay, now we're getting somewhere. The .htaccess Maker needs a bit of trial and error to tailor to your site and server. Please see https://www.akeeba.com/documentation/admin-tools-joomla/athtaccess500.html

Without having seen the site itself I can't know in advance which option(s) would need to be disabled. I can, however, make an educated guess that the most likely options to cause the problem would be “Protect against clickjacking”, “Reduce MIME type security risks”, or “Reflected XSS prevention”. If disabling these doesn't make a difference but disabling “Frontend protection” does then the problem may be what is described in How to determine which exceptions are required. This is something we've seen with some third party plugins which try to access files in the cache directory from the web, even though the cache directory is not supposed to be directly web-accessible.

> The problem is always, to follow the information 'rebuild the server config file' and rebuild it.

This is the same as going to the .htaccess Maker and clicking on “Save & Create .htaccess”. If you have not followed the steps to determine what's wrong with your .htaccess Maker configuration you will always end up with the same problem.

> The same happens now, if I move the webpage from my local system to the real web-adress.

When restoring the site you need to pay attention at the Site Setup page. There's an option about what to do with the .htaccess file towards the top, right-hand side of the main content area of the Site Setup page. Tell it to use the default .htaccess so you can access your site's backend.

Keep in mind that after transferring your site you need to at the very least edit the .htaccess Maker configuration to change the HTTP Host, HTTPS Host, and Directory at the bottom of the page. You may have to change other options as well, as I told you three days ago.

Remember, the .htaccess Maker settings are specific to the current installation of the site i.e. the host, web server configuration, domain, subdomain, and directory the site is installed in. Whenever you move your site (between domains, subdomains, subdirectories, or hosts) you need to check and update this information before regenerating the .htaccess file.

> The same happens, if I forget to delete the file 'autoload_psr4.php' inside of joomala cache

This file should be regenerated automatically using the installed extensions' information. If it doesn't get created you will need to make sure that the administrator/cache directory is writeable to PHP. If it gets created but results in a class not found error it means that something is not installed correctly. Install the extension referenced in the error message twice in a row, without uninstalling it before or in between, then delete the autoload_psr4.php file once more and reload any page of your site to have Joomla regenerate it.

You definitely need to change these three settings.

If you are using the same PHP version on both live and local servers without any special .htaccess code in the “Code to add at the bottom of the file” then of course you don't need to change anything about it.

As for other .htaccess Maker settings, it depends solely on the configuration of your server. If you get a 500 Internal Server Error on the live server you will have to change the .htaccess Maker settings to find out which one doesn't work on the live site. This is something you cannot know in advance and which cannot be detected automatically (otherwise we'd be doing that for you).