Libre Office writer gives me only a tiny icon
The Libreoffice window can nowadays be resized to a ridiculously small size:
(note within green mark).
Simply resize the window: move the mouse cursor over it until it changes to a resize cursor, and drag to resize the window. The new size will be remembered.
If you already deleted LibreOffice, then install it again with the command
sudo apt install libreoffice
or using the software center.