FIFA 21 online matchmaking system works based on two main factors, your division/skill rating and your location. The matchmaking system pairs you up with someone who is in the same division as you or has a similar number of FUT Skill Rating to you and preferably from the same location.
- Your Division / Skill Rating
- Your Region (Account region / IP address)
In FIFA Ultimate Team, your Skill Rating is important for matchmaking in Division Rivals matches. Reportedly, there are also some other factors that are considered for a matchmaking such as your team rating, team chemistry and team league.
Customising the matchmaking in FUT 21 is only limited to solo and co-op opponents where a co-op mode is available. This is available in online matches with co-op feature like FUT Rivals. To customise your matchmaking, you need to change the matchmaking settings by pressing L2/LT before you start finding an opponent.
In other game modes such as Online Seasons, you can change the settings for controls, club quality matching, club type and guests where a Matchmaking Settings option is available.