If you plan to enter, leave or transit through Malta with €10,000 or more in cash (or its equivalent in other currencies including commodities used as highly-liquid stores of value ) you must declare it to the customs authorities.
Since this procedure is not directly handled by Malta International Airport, you may obtain further information on
https://www.maltairport.com/passenger/security-passport-control/customs/#CD
and
https://customs.gov.mt/individuals/information-to-travellers-on-cash-declaration