An accessibility statement documents your conformance level, known limitations, and how to report a problem. It is required for public sector bodies in many jurisdictions and is good practice elsewhere, particularly when limitations are known and unresolved.
State the standard you target — usually WCAG 2.1 AA — and be honest about gaps.
Include a contact route for reporting barriers, and monitor it.
A statement claiming full conformance you have not tested is worse than none.