With the first solution (book), you are now reliant on hiding an entire book rather just a single piece of paper. If you lose your copy of the book, there is no guarantee you would find the exact same edition again and your coins will be lost. So that's a more difficult back up process and a single point of failure.

With the second solution (Github), you are now reliant on a third party to continue hosting your repo. If your account is banned, or their servers fail, or they shut down, etc., then your coins will be lost. So again, a more difficult process and a single point of failure.

If you want a set up in which your seed phrase can be compromised without resulting in immediate loss of your funds, then you would be far better off using a standardized method which does not have a single point of failure, such as either an additional passphrase or a multi-sig set up.