Flip a coin 11 times, turn the resulting number in to a BIP39 word from the word list. Repeat 22 more times.
Flip a coin 3 times, calculate the checksum using a permanently airgapped computer, pick the last word.
Write down on paper, import in to a wallet or iancoleman on your permanently airgapped computer to generate a receiving address (Optional: add in a passphrase and write that down on a separate piece of paper).
Whole thing can be done in 15-20 minutes.
Now all you need to do is do your SHA256 hash by hand to generate the checksum and you've got the complete no computer solution to generating a seed mnemonic Flip a coin 3 times, calculate the checksum using a permanently airgapped computer, pick the last word.
Write down on paper, import in to a wallet or iancoleman on your permanently airgapped computer to generate a receiving address (Optional: add in a passphrase and write that down on a separate piece of paper).
Whole thing can be done in 15-20 minutes.
It would however blow out your 15-20 minute time frame to probably closer to a day... having to do 64 rounds of SHA256 to get your final hash at a rough speed of 1 round per 15 minutes or so
There are just some things that are better left to computers
