I would like to farm a lot of friend points but the only way I’ve seen to do it is when you use another player’s monster or when yours is used and it only gives you 5 points. there is another method to get them quickly
No other way
you get more points by using monsters in your friends list.
Each time you enter a battle in some part of the online content it makes you available to select by other people in the game for a few minutes. So basically the more you play, the more you will get friend points from people selecting your monster. Additionally, you can try sharing different monsters to see if people select certain ones more than others.
The exploitive way to farm them is to enter biweekly missions (any of the 5 at the bottom) and then immediately surrender. You get the friend points from selecting a shared monster each time, even though you “lost” the fight. However, I do not recommend doing this because it’s so slow to farm friend points and what you get from them is not worth it.
You get 10 free chests a day, which is pretty much more than you can expect to get from earning friend points anyway. Just make sure you always claim those.