Generating unbiased numbers with a biased six sided die?
Each biased die result has >2.52 bits of Shannon entropy. Each unbiased die result has &lt;2.59. So 21 biased rolls have more entropy than 20 unbiased ones.

Alice can concatenate 21 biased results into $r$ and use $r_i = H(s||r||i) \bmod 6$ as the unbiased results, where $H$ is a hash function like SHA-256 and $s$ is a unique salt she decides just before rolling.

(If Alice wants to cheat, she must use >$2^{52}$ work to find an $s$ with biased outputs. If this is insufficient, roll more dice or decide $s$ in a way that does not allow this.)