📝Architecture risks can be added as spikes to backlog

Fairbanks2010, pp. 56–57

For agile projects, risks can be added to the common backlog (as spikes in scrum) and prioritized together with other features.

If Product Owner is not qualified to prioritize architectural risks, managing everything in a single backlog might get complicated. In that case, it might make sense to keep 2 backlogs and have a team suggest which risks are important to address.