This one is particularly hard. We are still working to get better at handling UX debts. It often gets lost in priorities and insertions. What helps us is making the debts visible. Having it listed on the same place where engineers and PMs have their tasks. Now, because it is visible, at some point it is going to see the light of the day, as opposed to gathering digital dust in your Sketch file.
Let’s say you are working on feature X, and due to time constraints only a MVP version of feature X gets shipped. Now, we should have this documented. Any time in the near future, when there is some work that touches on portions of feature X, it is a good time to bring it up in that sprint to check if that can be worked on.
Another way definitely is to plan with your PM in your 1:1s as to what among the debts take priority, where does it lie in terms of priority of other things on your plate now, and when it could be moved up the priority order.
Hope that answers your question!