How to fix a “damaged” macOS Installer

Showing the misconceptions and the truths of "This copy of macOS Installer is Damaged and can't be used to install macOS". The problem is not what you might think it is.
Link to create an install media: support.apple.com/en-us/HT201372
There are 2 possibilities of this error showing up.
1) Actually damaged installer
2) Expired macOS certificate (probably invalidated by Apple after some time)
Song: Jim Yosef & Alex Skrindo - Ruby [NCS Release]

[@OrangeGroupTech]

Did you guys actually know that this error was caused due to a signature verification error? Usually, unless it's pirated macOS doesn't corrupt on its own. Any questions about this signature error thing? Want to ask more? You can ask by replying to this comment below, and I'll try and answer them!

[@greeengiaant]

make sure to disconnect the internet otherwise the date will go back to the current one. Thank you man you are a life saver

[@Someone_Else190]

Happened for 2 installers on my MacBook Air 2012 but from launchpad

[@LimeGroupYT]

every time i hear this music i will remember the name Ruby==Rubly
you now what i mean

[@OrangeGroupTech]

Yes and that's why I used that music for the Rubly vid ;)

[@baogamingenglish6541]

Nice

[@CBFNetworksInternational]

Apple also makes accidents. Wrong signatures too

[@antikingtm6929]

8 comments and 8 likes? What The HECK ?

[@alluseri]

Liked

[@OrangeGroupTech]

Thanks!

[@3060PlayZ]

crapOS™

[@baogamingenglish6541]

Nice