After installing the latest Ubuntu I find that the icons in the applications folder (viz. /usr/share/applications), when opened in the Files application (Nautilus), come up as a blank page with a gear in the middle. If I try to open them I get a read only text box.
Best Answer
You are welcome to new brave world of modern GNOME Shell "desktop".
It is a bug 1819375 caused by upstream Nautilus simplification.
You have to use other fully-functional modern file-managers like Caja, Dolphin, Konqueror, Nemo, PCManFM or Thunar.
If you want to get normal fully-integrated non-surprising desktop back - remove GNOME Shell and install other normal desktop. You may want to follow my Q&A to do so. My recommendation is to install MATE DE instead.