We all know that Bitcoin's private key consists of 256 numbers or letters. However, with the adoption of bitcoin on a large scale. BTC accounts will be more and more. When the number of Bitcoin accounts is large enough, any 256 numbers and combinations of letters may be a private key. People can rely on guesswork to get bitcoin in their account.

i think the private key of Bitcoin should not be a fixed 256 bit. it should be able to change in an interval. the user can select the number of digits of its private key. For example: between 500 characters and 256 characters.

Why is it a public number: 256 bits?
The character of the private key is a privacy. The number of digits in the private key should also be a privacy.