preview Don't work in NC20.0.11

[Horizon2006]

I expected the result：

There seems like some problems after install files_markdown app refter to solution

environment:
nextcloud version: 20.0.11
php version : 7.4.21

1. apps
   the apps that enabled include below:
   
   

2. and according to the article solution

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cd /path/to/nextcloud/apps
wget https://github.com/nextcloud/files_texteditor/archive/v17.0.0.tar.gz
tar -xzf v17.0.0.tar.gz
mv files_texteditor-17.0.0 files_texteditor
find files_texteditor/ -type f -print0 | xargs -0 chmod 640
find files_texteditor/ -type d -print0 | xargs -0 chmod 750
sudo chown -R <webserver user>:<webserver user> files_texteditor
sudo chmod -R 777  files_texteditor 
rm v17.0.0.tar.gz

---

3. but the issue remains
   

Please guide me on this issue，thanks :)