i use trime on android and the default takes quite a while to get used to. for example, the symbol key that is usually on the bottom left corner is now a language switching key and the symbol key is one tiny key beside it. custom configuration seems like a pain and i haven’t done it. one of the defaults however comes with a menu that lets you type all sorts of symbols including greek, russian, japanese, IPA and mathematical operators. haven’t sen fcitx5 for android though