In FIFA 21 there are different ways to get packs. These can be earned through different game modes (Squad Battles, Weekend League, etc.), earned through Squad Building Challenges or simply bought.
Basically, the probability of pulling an outstanding player from packs is extremely low. The Youtuber ChrisMD has made an attempt in this regard and has invested around 5600 Euros in Fifa Packs. In the end he was able to generate about 10 million ingame coins from these packs. But to get anywhere near the price-performance ratio, he would have had to pull TOTGS Ronaldo 15 times. But this did not happen once.
From this follows: Don’t buy packs with coins, because this will only pay off in very rare cases.