The EFL Championship but it's every country/constituent country/overseas territory that is a FIFA member that has had a player with at least 1 appearance in the competition from 2004/05 onwards using a combo of my own personal knowledge, wikipedia & fellow redditors & I've listed a player from each
Afghanistan - Amin Nabizada
Albania - Anis Mehmeti
Algeria - Mehdi Leris
American Samoa -
Angola - Manuel Benson
Anguilla -
Antigua and Barbuda - Mikele Leigertwood
Argentina - Emi Martinez
Armenia -
Aruba -
Australia - Kenny Dougall
Austria - Dominik Frieser
Azerbaijan -
Bahamas -
Bahrain -
Bangladesh - Hamza Choudhury
Barbados - Thierry Gale
Belarus -
Belgium - Dennis Praet
Belize -
Benin - Andreas Hountondji
Bermuda - Nakhi Wells
Bhutan -
Bolivia -
Bosnia and Herzegovina - Anel Ahmedhodzic
Botswana -
Brazil - Neto Borges
British Virgin Islands -
Brunei -
Bulgaria - Ilia Gruev
Burkina Faso - Nasser Djiga
Burundi - Gael Bigirimana
Cape Verde - Ryan Mendes
Cambodia -
Cameroon - Harold Moukoudi
Canada - Cyle Larin
Cayman Islands -
Central African Republic
Chad -
Chile - Ben Brereton Diaz
China - Zhi Zheng
Chinese Taipei (Taiwan) - Tim Chow
Colombia - Oscar Estupinian
Comoros - Remy Vita
Congo - Christ Makosso
Congo DR - Edo Kayembe
Cook Islands -
Costa Rica - Bryan Ruiz
Cote D'Ivoire - Jean Michael Seri
Croatia - Ivor Pandur
Cuba - Onel Hernandez
Curacao - Leandro Bacuna
Cyprus - Marcus Edwards
Czech Republic - Ladislav Krejci
Denmark - Elias Jelert
Djibouti -
Dominica -
DPR Korea -
Dominican Republic - Junior Firpo
Ecuador - Jeremy Sarmiento
Egypt - Ahmed Hegazi
El Salvador
England - Jarrod Bowen
Equatorial Guinea - Emilio Nsue
Eritrea -
Estonia - Mart Poom
Eswatini -
Ethiopia -
Faroe Islands - Claus Bech Jorgensen
Fiji - Joshua Laqeretabua
Finland - Teemu Pukki
France - Moussa Sissoko
French Guiana -
Gabon - Jacques Ekomie
Georgia - Giorgi Chakvetadze
Germany - Caspar Jander
Ghana - Antoine Senenyo
Gibraltar - Scott Wiseman
Greece - Manolis Siopis
Grenada - Reuben Noble-Lazarus
Guadeloupe - Miguel Commiges
Guam -
Guatemala - Nathaniel Mendez-Laing
Guinea - Sory Kaba
Guinea Bissau - Alfa Semedo
Guyana - Isaiah Jones
Haiti - Wilson Isidor
Honduras - Maynor Figueroa
Hong Kong -
Hungary - Kornel Szucs
Iceland - Johann Berg Gudmundsson
India - Ryan Williams
Indonesia - Joey Pelupessy
Iran - Allahyar Sayyadmanesh
Iraq - Ali Al-Hamadi
Israel - Tomer Hemed
Italy - Marco Faraoni
Jamaica - Joel Latibeaudiere
Japan - Yu Hirakawa
Jordan - Tammer Bany
Kazakhstan - Alexander Merkel
Kenya - Collins Sichenje
Korea Republic - Bae Jun-Ho
Kosovo - Adthe Nuhiu
Kuwait -
Kyrgyzstan -
Laos -
Latvia - Kaspars Gorkss
Lebanon -
Lesotho -
Liberia - Alex Nimely
Libya -
Lithuania - Marius Zaliukas
Luxemborg - Danel Sinani
Macau -
Madagascar -
Malawi -
Malaysia -
Maldives -
Mali - Adama Noss Traore
Malta - Daniel Bogdanovic
Martinique - Jonathan Varane
Mauritania - Djeidi Gassama
Mauritius - Kevin Bru
Mexico - Raul Jimenez
Moldova -
Mongolia -
Montenegro - Milutin Osmajic
Montserrat - Lyle Taylor
Morocco - Imran Louza
Mozambique - Armando Sa
Myanmar -
Namibia - Ryan Nyambe
Nepal -
Netherlands - Crysensio Summerville
New Caledonia -
New Zealand - Liberato Cacace
Nicaragua -
Niger -
Nigeria - Bright Osayi-Samuel
North Macedonia - Darko Churlinov
Northern Ireland - Brodie Spencer
Norway - Sander Berge
Oman - Ali Al Habsi
Pakistan - Zesh Rehman
Palestine -
Panama - Jose Cordoba
Papua New Guinea -
Paraguay - Gustavo Caballero
Peru - Oliver Sonne
Philippines - Neil Etheridge
Poland - Bartosz Bialkowski
Portugal - Diogo Jota
Puerto Rico -
Qatar -
Republic of Ireland - Adam Idah
Romania - George Puscas
Russia - Pavel Pogrebnyak
Rwanda -
Samoa -
San Marino -
Sao Tome and Principe -
Saudi Arabia -
Scotland - John McGinn
Senegal - Iliman Ndiaye
Serbia - Alexander Mitrovic
Seychelles - Kevin Betsy
Sierra Leone - Kei Kamara
Singapore - Perry Ng
Slovakia - Tomas Rigo
Slovenia - Bojan Jokic
Solomon Islands -
Somalia - Abdi Sharif
South Africa - Kamohelo Mokotjo
South Sudan -
Spain - Adama Traore
Sri Lanka -
St Kitts and Nevis - Romaine Sawyers
St Lucia - Janoi Donacien
St Vincent and the Grenadines
Sudan - Mo Eisa
Suriname - Joel Piroe
Sweden - Kristoffer Nordfeldt
Switzerland - Almen Abdi
Syria -
Tahiti -
Tajikistan -
Tanzania -
Thailand -
The Gambia - Ebou Adams
Timor-Leste -
Togo - Yoan Folly
Trinidad and Tobago - Rio Cardines
Tunisia - Yan Valery
Turkey - Ozan Tufan
Turkmenistan -
Turks and Caicos - Steven Sessegnon
Uganda - Jordan Obita
Ukraine - Ivan Varfolomeev
United Arab Emirates
Uruguay - Carlos De Pena
US Virgin Islands
USA - Aidan Morris
Uzbekistan -
Vanuatu -
Venezuela - Fernando Amorebieta
Vietnam -
Wales - Jordan James
Yemen -
Zambia - Patson Daka
Zimbabwe - Marvelous Nakamba