How To Fix “Application Is Damaged, Can’t Be Used To Install MacOS” Failure on older Macs I hope this post will solve the issue if you run into it.

If you trying to install macOS High Sierra / El Capitan on an older like 2010 / 2011 or older.
You get the Failure-message mentioned above and if you try to create an macOS-USB-Stick and run the installation from it the message is like “MacOS could not be installed on your computer”.
Please check the following, did you redowload the macOS App? So the certificate issue is solved.

If so you should download the macOS App onto a current Mac Model fresh from AppStore and create a macOS-USB-Stick from the newer Mac, this should solve your issue with the AppStore Authentication, so you will be able to run the installation on your older Mac.