Peace be upon you. The esteemed Ayatollah Khamenei and Ayatollah Sistani (may Allah protect them) state that the criterion for this matter is based on common understanding. It is the responsibility of the individual to determine what is considered adornment, possibly by consulting experts. Generally, a regular mask is not seen as adornment unless it is a specific type or color. In that case, one should refer back to the aforementioned principle. May you be successful in all good.