Most of the addons featured below are custom data files that either tweak certain aspects of how the game works or add more depth to what's already there.
Thanks to Daveincid for helping me curate this list of addons.
Certain addons are available as packs which include multiple files. And since these files are created by different people, there are some cases of files that do similar things, so you'd have to choose just one to avoid data conflicts.
I'll briefly explain what all the different files do, where to find them, and when you need to make a choice to avoid possible conflicts.
So, let's get to it.
DLC for a More Realistic Football Manager 2021
Trophies MegapackAlmost 1200 real trophies to add to all playable nations in the game.
Trophy Podiums PackImprove the look of your trophy lift with competition specific podiums.
Press Conference BackgroundsCustom press conference backgrounds of teams and competitions.
Realistic Competition ColorsOver 400 competitions with inaccurate color schemes are updated and fixed.
Competition Colour FixA facelift to in-game competitions which are not licensed or are using their nations primary / secondary colours.
Nik33's Competition ColoursOfficial competition colours for UEFA comps and Copa Libertadores.
Match Day Experience
Fez's Enhanced Turf TexturesNew enhanced look of grass textures making the turf look more realistic.
3D Balls Mega Pack3D Ball Pack for over 150 Competitions! Use a ball for each competition!
Realistic WeatherReal-life annual weather data was used to optimize current weather patterns, and create new ones.
Better Crowd ColorsTurn that sea of orange to a sea of neutral colors. A mod for more realistic crowd colors.
Nik33's Club ColoursChanges club titlebar colours to their correct ones based on their logos and football tradition.
Audio Commentary PatchAudio Commentary, improved and adapted from previous versions. Includes crowd sounds.
Better Crowd SoundsRealistic Sound patch for crowd sounds that are better than the default ones. Only crowd sounds.
DaniDots 2021 Realism ModNo Attributes and No Stars to guide us on player assessment but there are ways to work this around.
FLUT Skin (alternative version)No visible attributes in FLUT's alternative skin version. An idea by richbell who also did the majority of the changes.
Real Names License FixFix fake name of competitions, clubs and awards with their real names in Football Manager 2021.
Nik33's Competition AbbreviationsUpdates 150+ competition abbreviations to match their licensed names.
Transfers & Finances
Transfer UpdateThis is the best Football Manager transfer update and it comes with daily repacks.
Current Currency Exchange RateReplicates the financial situation of all Nations more accurately to their current situation IRL.
Club Transfer PreferencesCertain clubs have a strong affinity for a specific nationality of players in the past and present. This is now a criteria in Visions of each Club.
Club Finances FixSugar daddy fix, finances of top clubs adjusted, added debts to clubs, adjusted Barcelona's financial situation.
Ticket Price AdjustmentsWorldwide ticket adjustments to avoid weak teams in financial poor nations are paying too high ticket-prices.
Realistic Transfer ValuesReal life transfermarkt data applied to 30 nations. Better than default Transfer Values.
Improved Market Values + Salaries + SponsorsAdjusted Market values to replicate transfer fees better. Increased potential Salaries for Top-players. Decreased salaries for some Nations.
Complete Pyramids Megapack by Weiry100% authentic footballing pyramids from 155 nations all around the world. Real Rules and Real Clubs.
Around The Globe Megapack by DaveRealistic leagues around the globe made in the advanced editor. With added focus on realism.
UEFA European Cups FixFix for teams from same nation being drawn against each other in qualifying rounds for European competitions.
Realistic InjuriesAdded 90 NEW injuries, and reworked 90% of injuries to be more logical.
Nik33's Extended Injuries SystemUpdates current injuries and adds 70 more to a total of 202 types for more diversity and realism, while slightly lowering some severe injuries odds.
Daveincid's Realistic InjuriesA better representation of injuries, as well as some new ones. You will get more injuries, more variety and more frustration.
Language Overhaul by majesticeternityAdded 80 New languages, 62 NEW Dialects. Edited 100 Nations and 1,500 Regions.
Geographics and LanguagesBetter distribution of place of birth's for newgens, influences sponsorship deals & fitness of players. Better representation of the diversity of nations, change the way how you are scouting for players, etc.
Media OverhaulAdds 4,240+ real media, 1,000 real journalists, 80 bookmakers, along with their styles & personalities.
Nik33's World Media packAbout 250 new media sources of every kind from all around the world.
Nik33's Agents packAdds more than 1.000 real life agents and their connections to 13.000+ players/clients, including every relevant relationship status as well.
Real Life Agents by pr0With specific attributes & clients adding more realism to the game.
Players & Staff
New Wonderkids by JG & SirTAVARESAn extensive database update that adds multiple young talented players to your Football Manager 2021.
New Wonderkids by pr0Newly created young players, aged U20 with a potential ability over -75, making them the future world class players.
Nik33's Career PlansAdds career plans to players/staff taking into account their real life choices, interviews and social media posts.
Nik33's Player PartnershipsAdds/updates player partnerships, a new feature that can add great real life partnerships like Kane/Son, Lukaku/Martinez etc.
Nik33's RelationshipsAdds more than 110 new relationships depending on player interviews, social media posts and other incidents. Also adds players' idols.
New Players & New Staff by pr0 (2 files)New players and new staff created who don't exist in the current database.
CA / PA Changes by pr0Adjusted attributes, current ability & potential ability numbers.
Nik33's Abilities & PersonalitiesUpdates player/staff attributes based on their real life season form and after extensive comparison between all top leagues' players. Fills many empty attributes and also deals with attribute anomalies.
Newgens & Reputation
Nik33's ReputationsUpdates reputations for Clubs, Nations, Competitions & adjusts nations' youth ratings.
Alternative Youth RatingChanges the National Youth Ratings, Game Importance and state of development for each Nation.
League Reputation FixesLowers the gap slightly between the Top-Nations and all the others in Europe. Boosts Top-Nations outside of Europe slightly.
Club Reputation FixesContains small reputation adjustments for some Brazilian, Argentinian and Mexican Teams.
Club Data FixesAdds a lot of missing data for almost 700 1st and 2nd division clubs in 150 nations worldwide.
Awards Overhaul160 New Awards, along with a entirely reworked reputation system.
Award FixesFixes all missing and illogical award-reputations in all nations and in all international competitions as well.
Derbies Overhaul550+ NEW Derbies added, reworked all to create realistic national and world reputations.
Worldwide Derby FixesAdds 300+ missing derbies from clubs and nations in over 50 nations.
Nations Agreements by DaveTheEditorAdds 24 agreements between nations.
Citizenship FixCorrections for 95 nations for "years to gain nationality".
Other Changes by pr0Changes in general which include second nationalities, affiliations between teams, new stadiums, favourite personel etc.
Nik33's Generic ChangesFixes player/staff info (DOBs, POBs, nicknames, histories, heights, weights etc), national team status, season stats, pref. squad numbers, language knowledge etc.
Data Tweaks by SirTAVARESAround +130,000 changes to improve the gaming experience. Also created people missing from the game.
Data BundlesMany of the addons listed above are included in the following bundles and you can grab each of them as a single download.
Realism Increase Megapack by Daveincid
Data Update Packs by pr0 & Transfers by FMTU
Nik33's Data Packs
I will keep updating this list from time to time to ensure it always reflects all the quality addons that raise the realism in Football Manager 2021.
If you think something's missing and should be added, let me know in the comments.