A user answered a question, the answer got many votes and was selected as the accepted answer; while it contains interesting elements, I find it's also partly inaccurate. How and where to discuss the technical details of the answer besides doing so in comments?
In the comments to the answer. That's the best, most direct place, because it's implied to pertain to that answer. If the back-and-forth comment discussion gets long enough, the SE system will automatically suggest you take the extended discussion to...
... Chat. When the discussion gets a lot of back-and-forth, it should head to chat, preferably its own chatroom.
If the answer is older, and maybe not likely to get engagement from the original author, you can opt to just edit the answer to make it correct. However, you run the risk of changing the answer's meaning. That path invites a possible revision war between you and the original author and/or community readers who disagree with the scope of your edits. So unless the edit is just making minor corrections (such as fixing typos, or easily-supportable technical fixes that are not opinion-based), I strongly do not recommend this route.
But really, the comments is the beginning place to note your objection. Comments aren't meant to last forever alongside an answer, but legitimate potential problems with an answer are almost never deleted by mods if those comments haven't been resolved / incorporated back into the answer.
If you put your notes/objections in any other place, they won't be easily correlated with the answer (i.e., they won't be seen).
The first thing to do if you think existing answers are incorrect is to write your own answer. You can even explicitly state why XXX doesn't apply, and the correct answer is therefore YYY. However, it's best not to mention the other answer directly, and certainly don't say things like "the answer above". Answer orders can change.
If you think the other answer is seriously wrong, then downvote it. While not required, you really should leave a comment explaining your objection. That gives the other answerer a chance to correct the mistake if he agrees, or to present his argument if he doesn't. It also lets others see what the disagreement is about.
You can also leave a comment without a downvote. Just don't go back and forth with the author. State your case, and leave it at that. A pissing contest just noises up the site.
One thing NOT to do is to edit the other answer if you disagree with its content. It's OK to edit someone else's post to fix obvious spelling, grammar, and formatting problems, but never to change the meaning.
To me a question about answers with 'interesting elements' but that are 'partly inaccurate' leaves a lot of room for interpretation. One of the difficulties when discussing this type of question is each person is free to imagine a different sort of answer. What makes this even harder is that the internet is not in the habit of describing the imagined basis for its answers...huh?
an answer with interesting elements and partial inaccuraciesdominated by the inaccuracies.
an answer with interesting elements and partial inaccuracieswhere the interesting elements and inaccuracies are balanced.
an answer with interesting elements and partial inaccuraciesdominated by the interesting elements.
It seems like I should probably have a different response to each. But I probably won't. Because I am like most people and will look at the answer and find a rationalization for my disposition and habits.
Maybe Duty Calls because I enjoy the sense of power doing my duty gives and what matters is the "you are wrong" inaccuracies and not the interesting elements. I hope not.
Using https://photo.stackexchange.com is supposed to be informative and fun. Historically, most people turn out to be wrong about many things. Fallibility is human nature but fortunately people are smart and recognize this intuitively and can be unsurprised by an answer that
an answer with interesting elements and partial inaccuracies and enjoy the interesting elements and not be upset by the partial inaccuracies...
...at least until there are voting arrows and comment boxes.
Because there are at least three different general (imagined) scenarios; an infinitude of possible actual cases; and a large but finite set of individuals acting from momentary emotional and intellectual states, trying to create one size fits all policy (and some StackExchange sites do that from Meta discussions not significantly larger than this) smells like a poor decision...again it is supposed to be informative and fun.
So my advice:
If reading the inaccuracies creates an emotional state where downvoting is cathartic, downvote. It's best for everyone.
If reading the inaccuracies creates an emotional state where commenting is cathartic, comment. Hopefully it is best for everyone.
It is o.k. to upvote something because it partially useful or interesting.
It is o.k. to fix something that is broken by editing it.
Making it easy to fix things is why everything can be edited by anyone.
The potential problems don't come from editing, they come from editing fights so don't engage in an edit war.
Be charitable because this is supposed to be informative and fun.
Upvotes don't cost anything.
To a first approximation the stakes are always low.
Use good judgement.