The manager window doesn't display any cookies. Searching doesn't appear to work. The "refresh" button doesn't populate a list of domains, or have any other obvious effect. In short, the addon doesn't seem to work.
ETA: Developer responded on the GitHub issues page and diagnosed the problem for me: the extension doesn't work with First-Party Isolation. I will re-test and update the review as soon as I can. Bumping to 5 stars in the meantime for the fast response and the excellent diagnosis.