WordPress sometimes shows updates / sometimes not / not saving several settings

Hey there,
I do have a very strange problem at the site https://koestler-fotografie.pd-design.at/.

#1 WordPress Updates. Sometimes the page shows, that there are updates. Most of the times not. When it shows updates and I try to make them, WordPress says that there is not update.

#2 When I try to save things in plugins, sometimes it does not work. e.g. I want to register the theme – ok – nothing happens. Or I want to register updraft+ – ok – refresh – old site.

I already deactivated all plugins and switched the theme to default. The update-situation is the same. When I only activate only one plugin – e.g. updraft+ and try to register – the same problem.

I already manually updated to wp 5.6. Same problem.

I really don’t know where that comes from.
Please help,
thanks very much!!

Here is the health-check-report:

### wp-core ###

version: 5.6
site_language: de_DE
user_language: de_DE
timezone: Europe/Vienna
permalink: undefined
https_status: false
multisite: false
user_registration: 0
blog_public: 0
default_comment_status: closed
environment_type: production
user_count: 5
dotorg_communication: true

### wp-paths-sizes ###

wordpress_path: /homepages/13/d180362090/htdocs/koestler-fotografie
wordpress_size: 463,16 MB (485662926 bytes)
uploads_path: /homepages/13/d180362090/htdocs/koestler-fotografie/wp-content/uploads
uploads_size: 127,95 MB (134166762 bytes)
themes_path: /homepages/13/d180362090/htdocs/koestler-fotografie/wp-content/themes
themes_size: 20,82 MB (21834109 bytes)
plugins_path: /homepages/13/d180362090/htdocs/koestler-fotografie/wp-content/plugins
plugins_size: 127,30 MB (133487478 bytes)
database_size: 11,38 MB (11927552 bytes)
total_size: 750,62 MB (787078827 bytes)

### wp-active-theme ###

name: The7 (dt-the7)
version: 7.7.7
author: Dream-Theme
author_website: https://dream-theme.com/
parent_theme: none
theme_features: core-block-patterns, menus, automatic-feed-links, post-thumbnails, title-tag, align-wide, responsive-embeds, wp-block-styles, editor-styles, editor-style, editor-color-palette, presscore-modules, widgets
theme_path: /homepages/13/d180362090/htdocs/koestler-fotografie/wp-content/themes/dt-the7
auto_update: Deaktiviert

### wp-themes-inactive (1) ###

Twenty Twenty: version: 1.2, author: WordPress-Team (latest version: 1.6), Automatische Aktualisierungen deaktiviert

### wp-plugins-active (17) ###

Admin Menu Editor: version: 1.9.5, author: Janis Elsts (latest version: 1.9.8), Automatische Aktualisierungen deaktiviert
Caldera Forms: version: 1.9.3, author: Caldera Forms, Automatische Aktualisierungen deaktiviert
Caldera Forms Anti Spam: version: 0.3, author: Yoohoo Plugins, Automatische Aktualisierungen deaktiviert
Classic Editor: version: 1.6, author: WordPress Contributors, Automatische Aktualisierungen deaktiviert
Custom Post Type UI: version: 1.8.2, author: WebDevStudios, Automatische Aktualisierungen deaktiviert
Disable REST API: version: 1.5.1, author: Dave McHale, Automatische Aktualisierungen deaktiviert
Disable XML-RPC Pingback: version: 1.2.1, author: Samuel Aguilera, Automatische Aktualisierungen deaktiviert
Easy Updates Manager: version: 9.0.7, author: Easy Updates Manager Team, Automatische Aktualisierungen deaktiviert
Enable jQuery Migrate Helper: version: 1.3.0, author: The WordPress Team, Automatische Aktualisierungen deaktiviert
Essential Grid: version: 3.0.9, author: ThemePunch (latest version: 3.0.10), Automatische Aktualisierungen deaktiviert
FileBird Lite: version: 4.3.1, author: Ninja Team, Automatische Aktualisierungen deaktiviert
Photography Management: version: 4.5.8, author: Codeneric, Automatische Aktualisierungen deaktiviert
The7 Elements: version: 2.3.1, author: Dream-Theme, Automatische Aktualisierungen deaktiviert
The7 Slider Revolution: version: 6.2.2, author: ThemePunch, Automatische Aktualisierungen deaktiviert
The7 Ultimate Addons for WPBakery Page Builder: version: 3.19.4, author: Brainstorm Force (latest version: 3.19.8), Automatische Aktualisierungen deaktiviert
The7 WPBakery Page Builder: version: 6.1, author: Michael M - WPBakery.com (latest version: 6.5), Automatische Aktualisierungen deaktiviert
UpdraftPlus - Backup/Restore: version: 2.16.41.24, author: UpdraftPlus.Com, DavidAnderson (latest version: 2.16.46.0), Automatische Aktualisierungen deaktiviert

### wp-plugins-inactive (3) ###

GDPR Cookie Consent: version: 1.9.5, author: WebToffee, Automatische Aktualisierungen deaktiviert
GDPR Cookie Consent Banner: version: 2.3.15, author: termly, Automatische Aktualisierungen deaktiviert
Wordfence Security: version: 7.4.14, author: Wordfence, Automatische Aktualisierungen deaktiviert

### wp-media ###

image_editor: WP_Image_Editor_GD
imagick_module_version: Nicht verfügbar
imagemagick_version: Nicht verfügbar
file_uploads: File uploads is turned off
post_max_size: 64M
upload_max_filesize: 64M
max_effective_size: 64 MB
max_file_uploads: 20
gd_version: 2.2.5
ghostscript_version: 9.27

### wp-server ###

server_architecture: Linux 4.4.236-icpu-055 x86_64
httpd_software: Apache
php_version: 7.4.13 64bit
php_sapi: cgi-fcgi
max_input_variables: 5000
time_limit: 50000
memory_limit: -1
max_input_time: -1
upload_max_filesize: 64M
php_post_max_size: 64M
curl_version: 7.64.0 OpenSSL/1.1.1d
suhosin: false
imagick_availability: false
pretty_permalinks: true

### wp-database ###

extension: mysqli
server_version: 5.7.30-log
client_version: mysqlnd 7.4.13

### wp-constants ###

WP_HOME: https://koestler-fotografie.pd-design.at
WP_SITEURL: https://koestler-fotografie.pd-design.at
WP_CONTENT_DIR: /homepages/13/d180362090/htdocs/koestler-fotografie/wp-content
WP_PLUGIN_DIR: /homepages/13/d180362090/htdocs/koestler-fotografie/wp-content/plugins
WP_MAX_MEMORY_LIMIT: -1
WP_DEBUG: false
WP_DEBUG_DISPLAY: true
WP_DEBUG_LOG: false
SCRIPT_DEBUG: false
WP_CACHE: false
CONCATENATE_SCRIPTS: false
COMPRESS_SCRIPTS: undefined
COMPRESS_CSS: undefined
WP_LOCAL_DEV: undefined
DB_CHARSET: utf8mb4
DB_COLLATE: undefined

### wp-filesystem ###

wordpress: writable
wp-content: writable
uploads: writable
plugins: writable
themes: writable

The page I need help with: [log in to see the link]