Here is the full list of all 99 Flag Collection achievements.
Macau
Hong Kong
People's Armed Police
the Imperial Japanese Navy (1889-1945)
People's Liberation Army
Plain White Banner
Plain Red Banner
Bordered White Banner
Bordered Red Banner
Plain Blue Banner
Bordered Blue Banner
Bordered Yellow Banner
Plain Yellow Banner
U.S. Air Force
U.S. Marine Corps
U.S. Coast Guard
U.S. Space Force
U.S. Army
U.S. Navy
Olympic Games
North Atlantic Treaty Organization
United Nations
Communist International
Commonwealth of Nations
International Atomic Energy Agency
Non-binary Pride Flag
Pansexuality Pride Flag
Polysexuality Pride Flag
Transgender Pride Flag
Leather Pride Flag (Black and Blue with Love)
International Bear Brotherhood Flag
Aromantic Pride Flag
Asexual Pride Flag
Bisexual Pride Flag
Genderfluidity Pride Flag
Genderqueer Pride Flag
Intersex Pride Flag
Lesbian Pride Flag
Rainbow Flag
Agender Pride Flag
Anarcho-syndicalism
African American Flag
Flag of the Earth
Lanfang Republic (1777-1884)
Ottoman Empire (1844-1923)
Ryukyu Kingdom (1429-1879)
France - Bourbon Restoration (1814-1815)
Nazi Germany (1935-1945)
Imperial Banner of the Holy Roman Emperor (1430-1806)
Union of Soviet Socialist Republics (1980-1991)
California Republic (1846)
Confederate States of America "Blood Stained Banner" (1865)
Republic of West Florida (1810)
National Government of the Republic of China (1928-)
Chinese Empire under the Qing dynasty (1889-1912)
Australia
Argentina
Brazil
Mexico
the United States
Canada
Vatican City
Portugal
Romania
Spain
Bulgaria
Greece
Italy
Russia
Ukraine
Hungary
Poland
Switzerland
Finland
Norway
Sweden
Austria
the Czech Republic
Germany
France
Ireland
the Netherlands
the United Kingdom
Denmark
Turkey
the United Arab Emirates
Belgium
Saudi Arabia
Israel
India
Thailand
Vietnam
Singapore
Malaysia
Indonesia
South Korea
North Korea
Japan
China