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