Usage of 誰でも and 誰にも

Question

I was recently corrected from using 誰でも→誰にも in this sentence:

それは決して否定できないことであって、（誰にも〇・誰でも？）分かる自明の理。

What's the difference between the two? This HiNative post says that 誰でも is usually used for affirmation while 誰にも can be used for either affirmation or negation. However, the above sentence does use 誰でも with an affirmative sentence. Does 誰にも simply sound more natural? If so, why?

Also, does this mean 誰でも can never be used with negation? Would a sentence like「誰でもできないこと」be wrong?

Answer 1

I asked my wife, a native speaker about your question, and she agreed with you. She said 誰でも is actually correct in your original sentence because it is affirming (肯定文) in your statement. 誰にも, on the other hand, would imply the opposite, a negative statement (否定文), and hence sounds strange in that context. 自明の理 requires agreement, something that is known by everyone.