Here is the full list of all 99 Flag Collection achievements.
People's Armed Police
the Imperial Japanese Navy (1889-1945)
People's Liberation Army
Bordered White Banner
Bordered Red Banner
Plain Blue Banner
Bordered Blue Banner
Bordered Yellow Banner
Plain Yellow Banner
Plain White Banner
Plain Red Banner
U.S. Coast Guard
U.S. Space Force
U.S. Army
U.S. Navy
U.S. Air Force
U.S. Marine Corps
Hong Kong
Macau
Olympic Games
North Atlantic Treaty Organization
United Nations
Communist International
International Atomic Energy Agency
Commonwealth of Nations
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)
Chinese Empire under the Qing dynasty (1889-1912)
National Government of the Republic of China (1928-)
Pansexuality Pride Flag
Polysexuality Pride Flag
Transgender Pride Flag
Leather Pride Flag (Black and Blue with Love)
International Bear Brotherhood Flag
Bisexual Pride Flag
Genderfluidity Pride Flag
Genderqueer Pride Flag
Intersex Pride Flag
Lesbian Pride Flag
Non-binary Pride Flag
Agender Pride Flag
Aromantic Pride Flag
Asexual Pride Flag
Rainbow Flag
Mexico
the United States
Argentina
Brazil
Australia
Canada
Russia
Ukraine
Bulgaria
Greece
Italy
Portugal
Romania
Spain
Vatican City
Poland
Switzerland
Norway
Sweden
Austria
the Czech Republic
Germany
Hungary
the Netherlands
the United Kingdom
Denmark
Finland
Turkey
the United Arab Emirates
Belgium
France
Ireland
Saudi Arabia
Israel
Thailand
Vietnam
India
Indonesia
Malaysia
Singapore
Japan
North Korea
South Korea
China