Использовать спред ...
и flat
:
const a = [[0, 45, 2], [3, 6, 2], [1, 5, 9]];
console.log(Math.min(...a.flat()));
Или вы можете использовать reduce
:
const arr = [[7, 45, 2], [3, 6, 2], [1, 5, 9]];
let r = arr.reduce((a, e) => Math.min(a, ...e), Infinity)
console.log(r);