Yes, even a dormant company should file a Confirmation Statement.

A Confirmation Statement is an annual statutory filing requirement that all companies must fulfil. It’s used to confirm if there have been any changes (e.g. SIC codes, shareholders/directors/people with significant control, shareholding, etc.) in the company in the past year, and if so, what these changes are.

Even if no change has been made, you must file one annually to confirm this to Companies House.