The prefer-array-some rule is not triggered when the .find() result is assigned to a variable:

const arr = [];
const hasFoo = arr.find(val => val === 'foo');
if (hasFoo) console.log('foo');

Obviously it shouldn't be triggered if hasFoo were to be used elsewhere for anything other than element existence checks, but if that's all it's used for, I'd expect it to trigger the rule.

Variable assignment of these element existence checks is useful when the predicate function is long, but also to generally make code read more prose-like.