It appears you will need a visa because you are not a citizen of Denmark (who have visa free entry to The Gambia) but of Afghanistan
Visa policy of the Gambia
Nationals of the following 104 countries and territories can visit the
Gambia without a visa for up to 90 days (unless otherwise noted)
Afghanistan is not on the visa free list, **neither is an exemption mentioned for permanent residents of visa free countries mentioned.
On their UK Embassy website it says:
Citizens of the United Kingdom, the Commonwealth, the Economic Community of West African States (ECOWAS) and other nations with a
reciprocal via abolition agreement with the Gambia do not require a
visa to enter the country; whether on holiday or on a business trip
not exceeding 90 days.