Preview of assets

Preview of assets on mouseover does not work.

  • I do not get a preview on asset folders
  • i do not get a preview on single images
  • i do not get a preview on office documents
    Output of ./bin/console debug: config pimcore assets:

Current configuration for “pimcore.assets”

versions:
days: null
steps: 10
use_hardlinks: true
icc_rgb_profile: ‘’
icc_cmyk_profile: ‘’
hide_edit_image: false
disable_tree_preview: false
default_upload_path: _hochgeladen
preview_image_thumbnail: null
tree_paging_limit: 100
image:
low_quality_image_preview:
enabled: true
generator: null
focal_point_detection:
enabled: true
thumbnails:
webp_auto_support: true
auto_clear_temp_files: true
video:
thumbnails:
auto_clear_temp_files: true

The path name for the default upload path is also not considered.
The changes in configuration have been made in ./app/config/config.yml and also in ./var/config/system.yml
Server has been restartet after changes being made. However, they do not show any effect.
Is there any other place I have to do configuration?