If you’ve tried to install Mac OS X El Capitan (10.11), and potentially other versions of OS X… you’ll run into a problem.
As it turns out, the certificates used to sign the OS X installer images stopped being valid sometime in 2019. And since these are older OS installers, Apple never renewed the certificates.
Thankfully, there is an easy solution. All you need to do is set go to “Utilities” in the installer, select the Terminal, set the date to something before the certificates expired, and then reboot and try again. This is the command to set the date (in this case, to January 1st, 2017):
It’s also worth mentioning, if you are using VMWare, be sure to disable time synchronization under Advanced in the settings, and also disconnect the network.