You get loyalty in FIFA 21 Ultimate Team by playing ten matches with a player.
Playing ten matches with specific players in FIFA 21 Ultimate Team squad battles will reward you with a loyalty bonus, as well as coins after every match.
You can play against the CPU on amateur to hopefully quicken up the process, but manually playing all ten matches would still eat up a few hours of your time.
However, there is a workaround via the loyalty glitch.
How to do the FIFA 21 loyalty glitch on PS4 and Xbox One
You perform the FIFA 21 Ultimate Team loyalty glitch on PS4 and Xbox One by starting an offline Squad Battles match.
Then, to follow through with the FIFA 21 Ultimate Team loyalty glitch on PS4 and Xbox One, you must simply quit the match as early as when the timer appears.
This will result in a 3-0 defeat and loss on your record, but you can overcome this by following the same method as above but disconnecting from the internet.
So, to perform the FIFA 21 loyalty glitch with no losses, you need to enter a match on squad battles, pause at least when the timer appears, and press the home button on your console’s controller.
Then proceed to either the PS4 or Xbox One network settings, disconnect from your internet, reconnect, and then return to FIFA 21.
An error message will appear saying that you lost connection from the EA servers, and the squad battles match will be finished.
Reconnect to the EA servers and Ultimate Team, and you should see that the game counted as a match played but that no loss has been given to your record.
Repeat this ten times to fully exploit the loyalty glitch.