What I've found to be most effective for program management is to set aside a maintenance team separate from the feature teams. The roadmap is then planned without counting anything for the maintenance team and they deal with bug tickets as they come in. Rotate the assignment periodically so that every developer has to occasionally spend a few months on the maintenance team.
Doesn’t this lead to problems like the feature team pushing buggy code and having no accountability or responsibility to deal with it?
My preference is to treat the defects like feature work, size and plan. Yes you might not get all the feature work done but the team is accountable for everything they make