Close them as duplicates of the first linked question
In general, almost all of those last set of questions seem like different subsets of a question asking "What abilities work in an antimagic field?" However, that question itself seems to be a duplicate of the very first question you linked: How do I know if an ability is magical?
The very purpose of that first question is to determine what is considered "magical", whether for the purpose of an antimagic field spell or similar effect, or for the purpose of determining what counts as "nonmagical damage" for armor of invulnerability and similar effects. Thus, most questions about whether something works in antimagic field will be duplicates of this question, to the extent that they're essentially asking whether that thing is considered "magical".
In fact, the second question you linked - How to decide if an effect is magical for Magic Resistance? - is also a duplicate of the first question. Its entire purpose is to ask how to determine whether an effect is magical, specifically for the purpose of the Magic Resistance trait.
Per the If an answer to question A can be found in question B, should we close A as duplicate of B? meta FAQ:
We close Question A as a duplicate of Question B only when all of the following is true:
- It's the same question, or Question A is already covered obviously as a subset of Question B. Obvious here means I can tell at a glance it's there.
- Question B has an obvious answer to Question A. Obvious here means I get a straightforward answer without hard searching — a couple of sentences buried in the middle of a post, or an answer which only sort of implies an answer to Question A, doesn't count as obvious.
- There is not some strong compelling reason to covering Question A alone, separately from Question B. (If the above bullet points are met this rarely happens.)
The idea here is it's the same question with an obvious answer. Someone redirected from Question A to B can see obviously why they were redirected and find a satisfactory answer.
In almost all of these cases, the "Is X magical?" is obviously covered as a subset of "How do I know if an ability is magical?". The game has a general way to define what's magical, so virtually any question asking whether a specific effect is magical is covered by the general question. The general question also has an answer that cites the mechanism for determining whether an ability is magical, so the second criteria is met.
Thus, questions that are simply asking specific versions of "Is X magical?" should be closed as a duplicate of the general question.
But there are a few exceptions
The last criterion quoted above, of course, is mainly where the exceptions I mentioned become relevant. For instance, the querent may have a specific reason to question whether an effect is magical even if it seems to meet the criteria quoted in the answer to the general question. The main example that comes to mind is one not linked in your post: Does ki count as magic for the purpose of an antimagic field, or is it only fluff?
Here, the reason is that the "fluff"/"flavor" text in the general description of the class clearly references ki as magical - but the Ki class feature never calls it magical, and a later class feature explicitly makes the character's unarmed strikes magical.
In these cases, the question should clearly address why the linked question doesn't already cover theirs. (This is already how we usually handle questions that seem like duplicates but where OP thinks their specific question might be an exception to the rule.)
Similarly, there may be cases where part of the question might just be "is X magical?", but there may be another aspect to it. For instance, there are two aspects to the following question, which can be handled differently: Can a warlock use Eldritch Smite in an antimagic field?
The first part of the question obviously asks whether Eldritch Smite is a "magical effect" that is suppressed by antimagic field, which is indeed a duplicate of the general question above. However, the other part of this question asks what happens when Eldritch Smite is suppressed, specifically with regard to the spell slot being expended or not. That question is currently distinct from the general case, because it's asking something different.
In cases where a question contains multiple parts or "sub-questions", only one of which is a duplicate of an existing question, the solution is often simple: edit the duplicate question out of the post, and refocus the post to ask the question that remains. This avoids unnecessary repetition, and allows answerers to focus on the real issue.
Of the last set of questions linked in your post, there currently seems to be just one question that should probably not be closed as a duplicate: Is the Channel Divinity feature negated in an antimagic field?
The reason this post is an exception is that OP's real confusion seems to have been revealed in their comment on the answer: "spells and magical effects [...] created by [a] deity" aren't suppressed, and Channel Divinity "channel[s] divine energy directly from your deity, using that energy to fuel magical effects." Since this is the source of their confusion, I've recommended they edit that into the question. It essentially turns it into an entirely different issue, asking not whether CD is magical but rather whether it counts as "created by a deity" - which is not a duplicate of the first question linked in your post.