While you can find unoffical street view coverage or at least photosphers from every single country in the world not every single country has offical coverage.
Countries with offical coverage are the following:
The countries marked in red are countries you will see all the time in Geoguessr and it is a safe bet to guess in one of them.
The countries marked in pink are quite rare and mostly trekker locations. I would suggest not guessing them unless there is a good hint it might be one of those countries.
The countries marked in blue you will almost never see unless you are playing a specific map that includes them. Don't guess these countries unless there is a good hint it might be one of those countries.
The countries marked in gray don't have official coverage and they should not be guessed unless the map includes unofficial coverage.
Africa
Algeria
Angola
Benin
Botswana
Burkina Faso
Burundi
Cabo Verde
Cameroon
Central African Republic
Chad
Comoros
Côte d’Ivoire
Democratic Republic of the Congo
Djibouti
Egypt
Equatorial Guinea
Eritrea
Eswatini
Ethiopia
Gabon
Gambia
Ghana
Guinea
Guinea-Bissau
Kenya
Lesotho
Liberia
Libya
Madagascar
Malawi
Mali
Mauritania
Mauritius
Mayotte
Morocco
Mozambique
Namibia
Niger
Nigeria
Republic of the Congo
Réunion
Rwanda
Saint Helena
São Tomé and Príncipe
Senegal
Seychelles
Sierra Leone
Somalia
South Africa
South Sudan
Sudan
Tanzania
Togo
Tunisia
Uganda
Western Sahara
Zambia
Zimbabwe
Antarctica
Bouvet Island
French Southern and Antarctic Lands
Heard Island and McDonald Islands
Asia
Afghanistan
Bahrain
Bangladesh
Bhutan
British Indian Ocean Territory
Brunei
Cambodia
China
Christmas Island
Cocos (Keeling) Islands
Hong Kong
India
Indonesia
Iran
Iraq
Israel
Japan
Jordan
Kazakhstan
Kuwait
Kyrgyzstan
Laos
Lebanon
Macao
Malaysia
Maldives
Mongolia
Myanmar
Nepal
North Korea
Oman
Pakistan
Palestine
Philippines
Qatar
Russia
Saudi Arabia
Singapore
South Korea
Sri Lanka
Syria
Taiwan
Tajikistan
Thailand
Timor-Leste
Turkmenistan
United Arab Emirates
Uzbekistan
Vietnam
Yemen
Europe
Åland
Albania
Andorra
Armenia
Austria
Azerbaijan
Belarus
Belgium
Bosnia and Herzegovina
Bulgaria
Croatia
Cyprus
Czech Republic
Denmark
Estonia
Faroe Islands
Finland
France
Georgia
Germany
Gibraltar
Greece
Guernsey
Hungary
Iceland
Ireland
Isle of Man
Italy
Jersey
Kosovo
Latvia
Liechtenstein
Lithuania
Luxembourg
Malta
Moldova
Monaco
Montenegro
Netherlands
North Macedonia
Norway
Poland
Portugal
Romania
San Marino
Serbia
Slovakia
Slovenia
Spain
Svalbard and Jan Mayen
Sweden
Switzerland
Turkey
Ukraine
United Kingdom
Vatican City
North America
Anguilla
Antigua and Barbuda
Bahamas
Barbados
Belize
Bermuda
British Virgin Islands
Canada
Cayman Islands
Costa Rica
Cuba
Curaçao
Dominica
Dominican Republic
El Salvador
Greenland
Grenada
Guadeloupe
Guatemala
Haiti
Honduras
Jamaica
Martinique
Mexico
Montserrat
Nicaragua
Panama
Puerto Rico
Saint Barthélemy
Saint Kitts and Nevis
Saint Lucia
Saint Martin
Saint Pierre and Miquelon
Saint Vincent and the Grenadines
Sint Maarten
Trinidad and Tobago
Turks and Caicos Islands
United States
United States Virgin Islands
Oceania
American Samoa
Australia
Cook Islands
Fiji
French Polynesia
Guam
Kiribati
Marshall Islands
Micronesia
Nauru
New Caledonia
New Zealand
Niue
Norfolk Island
Northern Mariana Islands
Palau
Papua New Guinea
Pitcairn Islands
Samoa
Solomon Islands
Tokelau
Tonga
Tuvalu
United States Minor Outlying Islands
Vanuatu
Wallis and Futuna
South America
Argentina
Aruba
Bolivia
Brazil
Caribbean Netherlands
Chile
Colombia
Ecuador
Falkland Islands
French Guiana
Guyana
Paraguay
Peru
South Georgia and the South Sandwich Islands
Suriname
Uruguay
Venezuela