Are questions regarding password cracking on-topic?
This could include passwords of archives such as ZIP, RAR, 7Z etc. but also cracking of OS passwords like NTLM hashes or a Linux
Yes, such questions are on-topic as long as they fulfill our usual requirements.
there are legitimate uses of password crackers, e.g. when you have forgotten your own password or when testing the security of your application
like in this question about breaking the terms and conditions, we are not lawyers, especially not for all countries around the world
When the use case seems close to illegal, we can still mention that, perhaps downvote, simply do not post an answer and leave the final decision of whether or not to use such a tool up to the OP.
Knowledge is always good, whether learning how to crack passwords, how to write malware, how to do phishing. Maybe you are a computer security student, or an ethical hacker. Maybe you are just curious.
For instance, metasploit is a legit company, if someone uses it for bad activities, it's his fault, metasploit shouldn't stop creating software simply because it might be used for bad activities.
Similarly, universities shouldn't stop teaching nuclear physics because some dude might end up creating an A-bomb for N. Korea. Knowledge about any subject is never bad. SE network should spread knowledge.