In simple terms, the ciphertext and substitution table are publicly displayed, and without knowing the rules, it is impossible to reverse deduce the plaintext. Even if the plaintext, ciphertext, and substitution table are publicly displayed, it is impossible to reverse deduce the rules. I will give an example to illustrate this later. 

 Let's take an example

you have 12 seed words in the following order:

anger animal check effort eight episode just oppose pig possible question sea

By the way, this happens to be one set of possible solutions to your challenge.

I re-encrypted them with my password card as below
https://image.nostr.build/3a4d3f8a72c7cfe3ff77eaa7d256e1b4743024637b5ef0dad4ac0ba137d6d0ad.jpg
 to get the following strings:

h+ike2Tk2hK9!%%+%@7#S9fVhMV^pVMV!h9Tb=2S9&Xe+hs8~npf5eMss

I can write this string of characters on a piece of paper and put it anywhere in the public domain, along with my password card.

If no one else knows the plaintext and substitution rules, then your seed words are safe.

And even you yourself know the plaintext of the 12 words, and you know the ciphertext, and you have this substitution table from my password card, but you still can't backtrack my substitution RULES.

Once you can do that, guess my substitution rules, you can restore another  ciphertexts that I have written on paper and made public:

5hK9!spT&=h+Vs%9K9bXh+hY7fM2&8%+X@e9M2fVhMXspVT^h%Ss@2h+XP

You'll find this is another group of MY seed words:

XXXXXX XXXXXXX XXXXXXX XXXXXX XXX XXXXX XXXXX XXX XXXXXX XXXXX XXXXXX XXXXXXXX

By the way, this group of seed words is another set of possible solutions to your challenge.

can you make it?

As you can see, the key to security becomes the RULES, and it's always easier to memorize the rules than it is to memorize individual ciphers one by one, so I use this card to manage all of my high-strength passwords over 8 years, and I'm sure it can be used to keep the seed words safe as well.  

 Tell that to @fiatbrecher