On several occasions, I have attempted to install various MacOS versions using the appropriate installer file (downloaded from the App Store) only to be told they are corrupted and can’t be used. Again, these are the installer files (5 - 6 GB) that I obtained on the App Store and then saved to a thumb drive for future use. I have been successful a couple of times as well using (I think) the same method.
Any idea as to why these files won’t work. Is is related the signing certificates? Is there a way to fix this?