Max Chemistry is a friendly game mode in FUT which gives your players a maximum chemistry boost.
This mean every player on your squad will have a maximum chemistry number. This also applies to your opponent.
By playing this game mode, your players will get a max chemistry amount of 10 (Green) even though they are not matching with each other. For example, if you have an Italian CB from Serie A and your GK is an Irish keeper from Premier League, the chemistry between these two player will be 10 (Green) on the pitch.
How to Play the Max Chemistry Mode
Max Chemistry friendly mode is available in FUT 21 > PLAY tab > FRIENDLIES (Couch Play / Play Online / Play A Friend).