Order of “not” with infinitive
It's OK to make mistakes; it's not OK not to learn from them.
What kind of grammar structure is this? Could I use "to not" as a replacement for the bold words?
You can certainly say . . . it's not OK to not learn from them. However, bear in mind that there are still people around who mistakenly believe that such a construction is a split infinitive and should be avoided. (They are mistaken because the particle to is not part of the verb so there’s nothing to split.) If you think your readers or listeners may be of this persuasion, you may want to put it differently to deflect the distraction that any adverse comments might prompt. An alternative might be . . . it's not OK to fail to learn from them.
The words "to not learn" in this context constitute something called a "split infinitive" - that is, the words of the infinitive "to learn" have been separated (sorry, @Barrie, I disagree with you on this). Traditionally, people were taught to avoid split infinitives; but sometimes, it's more natural to split an infinitive than not to. That is, split infinitives are no longer considered a grammatical error.
In this particular case though, it's easy to avoid splitting the infinitive - just write "not to learn". There's no reason to write "to not learn", and it's better and cleaner to write "not to learn".