A combination of the services listed in the game, because I manually edit both the model and resulting sprites.
If you're willing to put in some effort, you could also use Flux Kontext or Nano Banana for novel view synthesis, and then scale the resulting images down to 32 pixels height and clip the alpha:
Instructions used:
Create a frontal view of this character. I understand that the character is already facing the camera, but it should be even more direct. Create a left-facing view of this character. Create a back view of this character. Create a right-facing view of this character.