Regarding how to manually create a set of truly random mnemonics as a cold wallet, I referred to some methods on the Internet, selected 2048 mnemonic databases on github, and used the method of rolling dice. Roll the dice four times for each letter to form a Four digits, and then find the corresponding serial number letter of the mnemonic database on github. If the result is greater than 2048, subtract a multiple of 2048 until the result is less than or equal to 2048. This ensures that each letter of the mnemonic database serial number is selected. The probability of arrival is almost equal. After the first eleven letters are determined, the letters are randomly selected and the check digits are tried one by one. Generally, a suitable check digit can be found after an average of about ten times.