Is it against the rules to post answers that solve problems without using the command line?
I posted an answer here, but apparently solving a problem using Synaptic Package Manager is unacceptable.
No, of course you can post an answer that details how to do anything by any available means.
However, I also don't think the Mod comment actually state a very clear or understandable reason why the answer is deleted.
I believe the reason your answer does not qualify as such is because it lacks sufficient detail on how to do what you state. If you improved the answer by adding 1) How to install
synaptic and 2) How to do the exact steps that solved the issue for you, then your answer could be undeleted.
As Artur said, posting answer that don't use the command line is absolutely fine. However, your post wasn't actually an answer. After your edit which removed the suggestion of the already existing feature of unattended upgrades, this is the entirety of your answer:
I have had the same problem. I was able to do the updates through Synaptic Package manager.
OK. So what is this tool? How does one get it? What do you need to do with it to get around the problem? How do you use it?
We expect answers to have more detail here and explain what needs to be done. The question doesn't actually ask a specific question, which is unfortunate, but a perfect answer would explain what this "prepared update" thing is, what causes it, how to avoid it in the future, and how to get around it. Your answer only suggests that using some tool in some unspecified way might be able to do some undefined improvement.
I know it seems like we're all a bunch of nitpicking pedants. And, frankly, many of us are. I certainly am! But the goal of thee sites is to provide a useful library of questions and answers to help future visitors. This is why we're so persnickety about "quality" and rules. It seems weird at first, but the simple truth is that these rules, and this pedantry, result in a useful resource and are what stops us from becoming the noisy mess of the classic forums.