The obvious answer here is Genshin but Guardian Tales is a very slept on gacha game. I find the pixel art very cute and nostalgic and they are very generous with gems that you can use for summoning. They also have a good pity system to get what you want. I'm completely free to play and I'm currently at the second highest rank in the PvP game modes and am only missing 2 of the 5* characters. Additionally, the story is extremely deep and makes you fall in love with the characters. This is also not mentioning all the pop-culture, movie, and anime references there are in the game. If you haven't tried it I encourage you do! It's my favorite mobile game thus far.