Questions can be migrated at Closing>Off-Topic>Migration, but only to the targets "Unix and Linux Meta" and "Stack Overflow", but not "Ask Ubuntu".
Ask Ubuntu is a very probable target, simply because there are questions that are not technically wrong here, but much better suited for Ask Ubuntu.
Above and beyond Why can we not vote to migrate a question to superuser.com?, there's some previous history here:
(2010) - How did Unix/Linux survive Area51?: "Eventually there was a vote about merging, with Unix voting for merging, Ubuntu voting not to ... the sites ended up deciding to only migrate from Ubuntu to Unix if the question doesn't apply to Ubuntu, and only from Unix to Ubuntu if the question doesn't apply to any distro but Ubuntu"
(2010) - Bonus reading: StackOverflow Blog: "Unix and Ubuntu: Why Both?"
(2011) - Migrate Ubuntu-specific questions to AskUbuntu?: "So I'd only migrate questions where the question is extremely and unavoidably Ubuntu-centric, and cannot be generalized to other *nixes in any meaningful way."
(2013) - Ubuntu specific questions: "I think would be risky, because we get an awful lot of "belongs on Ask Ubuntu" flags because the asker happens to be using Ubuntu, even if the question has nothing to do with Ubuntu specifically; I think we'd end up migrating a lot of generic Linux posts over there."
(2014) - How to identify which questions belong to which site?: (see the picture there)
The last time we migrated a question to Ask Ubuntu from here was on August 15th of 2019 after the post was flagged by its author. It remains open and upvoted on Ask Ubuntu.
We also have the Help Center post, What topics can I ask about here? which says:
Note that Ubuntu posts are a special case. If your question applies to Ubuntu only, or you're looking for answers that are Ubuntu-specific, you should post it on the Ask Ubuntu Stack Exchange site. If your question applies to other distros or you welcome more generic solutions, you're in the right place here.
