But the point is the bias if really high would be detected in creating the 24 seed words.

Obviously a 25%  roll of any of the numbers ie 25 of 100 would show bias reliably.

If any number on the die is rolling at 25% you will see it. As you are main a lot of rolls to get your seed of 24 words.

If the number 1 is 25%

and the other 5 numbers are 15% each, As determined with 100000 test rolls.

There are formulas that would show your bits of entropy.

and yeah it won't be 256 like a true 24 word seed. But it still would be really good amount bits.