Bei der Einstellung "URL-Rewrite nutzen", erhalte ich einen Fehler 404. Laut IONOS würde das an mir liegen und nicht an denen.

##
# @package    Joomla
# @copyright  (C) 2005 Open Source Matters, Inc. <https://www.joomla.org>
# @license    GNU General Public License version 2 or later; see LICENSE.txt
##


##
# READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE!
#
# The line 'Options +FollowSymLinks' may cause problems with some server configurations.
# It is required for the use of Apache mod_rewrite, but it may have already been set by
# your server administrator in a way that disallows changing it in this .htaccess file.
# If using it causes your site to produce an error, comment it out (add # to the
# beginning of the line), reload your site in your browser and test your sef urls. If
# they work, then it has been set by your server administrator and you do not need to
# set it here.
##


## MISSING CSS OR JAVASCRIPT ERRORS
#
# If your site looks strange after enabling this file, then your server is probably already
# gzipping css and js files and you should comment out the GZIP section of this file.
##


## OPENLITESPEED
#
# If you are using an OpenLiteSpeed web server then any changes made to this file will
# not take effect until you have restarted the web server.
##


## Can be commented out if causes errors, see notes above.
Options +FollowSymlinks
Options -Indexes


## No directory listings
<IfModule mod_autoindex.c>
IndexIgnore *
</IfModule>


## Suppress mime type detection in browsers for unknown types
<IfModule mod_headers.c>
Header always set X-Content-Type-Options "nosniff"
</IfModule>


## Protect against certain cross-origin requests. More information can be found here:
## https://developer.mozilla.org/en-US/docs/Web/HTTP/Cross-Origin_Resource_Policy_(CORP)
## https://web.dev/why-coop-coep/
#<IfModule mod_headers.c>
#	Header always set Cross-Origin-Resource-Policy "same-origin"
#	Header always set Cross-Origin-Embedder-Policy "require-corp"
#</IfModule>


## Disable inline JavaScript when directly opening SVG files or embedding them with the object-tag
<FilesMatch "\.svg$">
<IfModule mod_headers.c>
Header always set Content-Security-Policy "script-src 'none'"
</IfModule>
</FilesMatch>


## These directives are only enabled if the Apache mod_rewrite module is enabled
<IfModule mod_rewrite.c>
RewriteEngine On


## Begin - Rewrite rules to block out some common exploits.
# If you experience problems on your site then comment out the operations listed
# below by adding a # to the beginning of the line.
# This attempts to block the most common type of exploit `attempts` on Joomla!
#
# Block any script trying to base64_encode data within the URL.
RewriteCond %{QUERY_STRING} base64_encode[^(]*\([^)]*\) [OR]
# Block any script that includes a <script> tag in URL.
RewriteCond %{QUERY_STRING} (<|%3C)([^s]*s)+cript.*(>|%3E) [NC,OR]
# Block any script trying to set a PHP GLOBALS variable via URL.
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block any script trying to modify a _REQUEST variable via URL.
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
# Return 403 Forbidden header and show the content of the root home page
RewriteRule .* index.php [F]
#
## End - Rewrite rules to block out some common exploits.


## Begin - Custom redirects
#
# If you need to redirect some pages, or set a canonical non-www to
# www redirect (or vice versa), place that code here. Ensure those
# redirects use the correct RewriteRule syntax and the [R=301,L] flags.
#
## End - Custom redirects


##
# Uncomment the following line if your webserver's URL
# is not directly related to physical file paths.
# Update Your Joomla! Directory (just / for root).
##


RewriteBase /


## Begin - Joomla! core SEF Section.
#
# PHP FastCGI fix for HTTP Authorization, required for the API application
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
# -- SEF URLs for the API application
# If the requested path starts with /api, the file is not /api/index.php
# and the request has not already been internally rewritten to the
# api/index.php script
RewriteCond %{REQUEST_URI} ^/api/
RewriteCond %{REQUEST_URI} !^/api/index\.php
# and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn't directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the /api/index.php script
#RewriteRule .* api/index.php [L]
# -- SEF URLs for the public frontend application
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index\.php
# and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn't directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
#
## End - Joomla! core SEF Section.
</IfModule>


## These directives are only enabled if the Apache mod_rewrite module is disabled
<IfModule !mod_rewrite.c>
<IfModule mod_alias.c>
# When Apache mod_rewrite is not available, we instruct a temporary redirect
# of the start page to the front controller explicitly so that the website
# and the generated links can still be used.
RedirectMatch 302 ^/$ /index.php/
# RedirectTemp cannot be used instead
</IfModule>
</IfModule>


## GZIP
## These directives are only enabled if the Apache mod_headers module is enabled.
## This section will check if a .gz file exists and if so will stream it
##     directly or fallback to gzip any asset on the fly
## If your site starts to look strange after enabling this file, and you see
##     ERR_CONTENT_DECODING_FAILED in your browser console network tab,
##     then your server is already gzipping css and js files and you don't need this
##     block enabled in your .htaccess
<IfModule mod_headers.c>
# Serve gzip compressed CSS files if they exist
# and the client accepts gzip.
RewriteCond "%{HTTP:Accept-encoding}" "gzip"
RewriteCond "%{REQUEST_FILENAME}\.gz" -s
RewriteRule "^(.*)\.css" "$1\.css\.gz" [QSA]


# Serve gzip compressed JS files if they exist
# and the client accepts gzip.
RewriteCond "%{HTTP:Accept-encoding}" "gzip"
RewriteCond "%{REQUEST_FILENAME}\.gz" -s
RewriteRule "^(.*)\.js" "$1\.js\.gz" [QSA]


# Serve correct content types, and prevent mod_deflate double gzip.
RewriteRule "\.css\.gz$" "-" [T=text/css,E=no-gzip:1]
RewriteRule "\.js\.gz$" "-" [T=text/javascript,E=no-gzip:1]


<FilesMatch "(\.js\.gz|\.css\.gz)$">
# Serve correct encoding type.
Header set Content-Encoding gzip


# Force proxies to cache gzipped &
# non-gzipped css/js files separately.
Header append Vary Accept-Encoding
</FilesMatch>
</IfModule>