I used to use Kanji LS (for ios and android) for practising writing. I’d like to say i use it for practising writing, but I got lazy and mostly used it for pre-practising the next levels kanji before level up.
It’s a payed app, but it’s not too expensive and you only pay once. I also made custom kanji-sets with custom kanji-meanings to fit with wanikani’s levels and wanikani’s kanji-meanings.