I think running an automated script over each new question to look out for keywords like
kali, etc. is a bad idea and would result in far too many false positives. Reviewing all of them would mean more work than just letting them appear on the main site until somebody comes by and flags it or votes to close.
On the other side, we have one great thing beside title and question body: tags!
There are already mechanisms to block specific tags so that a red speech bubble is appearing if you try to enter one and you can not submit the question - just try to ask a question tagged with installation:
What should be possible to implement and set up is to block specific off-topic tags if they are not combined with others that make them on-topic again.
For example we can block tags mentioning off-topic OSes like
kali unless they are combined with a tag telling us in what way those systems are related to Ubuntu here, e.g.
Of course this means somebody has to create and maintain a list of potentially off-topic tags and their on-topic-making partner tags. Therefore this suggestion will probably not work either.
But instead of blocking those tags, we could also just display this red speech-bubble with a warning, like
Please remember that this site is about Ubuntu and its official flavours only. If your problem is mainly about Windows, ask it on Super User instead, if it's about any other Linux distribution, you're welcome on Unix & Linux. If you're unsure whether your system is on-topic here, check whether it's on the list of official Ubuntu flavours.
This definitely gains the user's attention and also redirects them to the proper place to ask if they recognize their mistake themselves. It would be a great advantage if clicking a link in this bubble directly takes the user to the other site's "Ask Question" page and copies their already entered content over as well.
With this approach, you have no additional reviews and users could still post their question anyway if they think it should be on-topic here, but we can probably catch a big percentage right before they reach the main site. We also provide clear and understandable, user-friendly guidance instead of simply closing their question as off-topic later.