Arduino IDE / Specified folder/zip file does not contain a valid library I trying to add library here but it doesn't seem to work https://github.com/esp8266/Arduino

This happens
"Specified folder/zip file does not contain a valid library"

This problem make me no longer upload any library. any solution about this??
Manual installation does not either.
You don't install that repository as a Arduino library.

Read the README file in that repo. It explains how to install it using the Arduino IDE Board manager. That's the correct way to install it.