If the ramifications of a ruling made by an officer not entitled to the office are small, such as for example the "unqualified" officer renders ONE ruling that affects ONE person, the courts will undo the little ruling, and will not invoke the de facto officer doctrine.
The larger the ramifications, the bigger the mistake in allowing an unqualified person to attain office, the more likely the courts will wave their hands, invoke "de facto officer doctrine," and let somebody else deal with the fallout.
Also the bigger the mistake, the more likely the court is to either not take the case, or rule that no mistake was made.
Judges get their positions largely based on gaslighting skills; and on a willingness to compromise principle to preserve status quo. If they didn;t possess those qualities, they would not be approved.
Well, that sounds horrible.
Suppose, for instance, that the non-eligible officer committed massive crimes, and is arrested for those crimes. Of course, this whole situation is unprecedented, but how do you think that might affect the outcome?
And add to that the fact that many others conspired with him to commit criminal fraud so he could get elected?