Ok, let me explain. Easiest way I know is to use a seedsigner to create an airgapped wallet. How to build your own one is documented here:
After assembling your seed signer, you have multiple options to generate a seed. Note: as soon as an algorithm is involved, it’s loses safety because an algorithm can be cracked. So creating entropy by yourself means that you create your seed by your own, with a coin or a dice and pen and paper. Good way to do this is documented here:
https://estudiobitcoin.com/do-you-trust-your-seed-dont-generate-it-yourself/
When you got your seed and the seedsigner ready, you ideally set up your own node and use smth. like specter, because specter and seedsigner work together well. Find a tutorial here (there are a lot of other options available though):
Last thing would be to stamp your seed on a plate, there are different possibilities listed here or just google for available options:
https://jlopp.github.io/metal-bitcoin-storage-reviews/
And a final note: never trust the bank! Rather you should get your own safe!
There are tons of related information available. You can start with the info above and find your way to bulletproof custody. 🧡