Madden 21 does make some strange choices when it comes to its menu design. Even one of its best modes, The Yard, falls victim to this, as well. For instance, although there is no mention of how to play with friends in the game mode, it is entirely possible and can be done as long as both of you have created your own characters. For the moment, you cannot go up against your friends, but you are able to have them as teammates.
The first major thing you must know is that players can play co-op versus either the CPU or strangers online. The option to choose which one you want is found in the main menu. After, the game will tell you your party size, but if you actually go and click on the number, you can change and move it up to three. From there, you will be prompted to invite others by pressing triangle, for PlayStation users, or Y, for those on Xbox.
You should see the friend you want to invite here. However, the list of friends only shows those playing Madden 21. So, if there are any problems, make sure your potential teammate has the game booted up. For the best chance at success, ensure that your friend’s character is a different position than yours and that their prototype is appropriately leveled. If not, you may want to look for different teammates.
Related: Does Madden 21 support cross-play?