which is not necessarily a requirement popping up just before reducing technical debt.

Most likely this requirement was there from the beginning (serious project) or introduced later (like a prototype that had to go to production). But refactoring can occur multiple times at any time

Yes that is my point too. it is a continuous requirement. you could have a boss knock on your cube everymorning and say “new requirements! if any packages need upgrading for security today or if there are any customer bug reports today work on them!” but it would get boring.