IMO, the best modern mobile game is Vampire Survivors, by far. A lot of mobile game, even the good ones, are at least somewhat predatory in their monetization and all (what a surprise to hear!!) but VS is like the complete opposite. I admittedly did not play in a while but it is such an addicting and nice gameplay loop, and you really feel like you get your money's worth. I also heard that they apparently have a Warhammer spinoff incoming?? Dunno if it's a mobile game or not though.
There used to be this really old mobile game I loved WAYS back , though. It was kind a voxel based monster battler where you made your own monsters using a builder and kind of battled out in a linear dungeon? I am super fuzzy on the details but I remember loving it a ton.