I know a lot of the reviews here express discontentment with TextExpander’s support on iOS. I hear that, but - as a Bear and Drafts user - I rarely encounter this as a limitation. I also use an external keyboard with my iPhone, though, which makes calling the TextExpander keyboard anywhere else somewhat inconvenient. (Keyboard switching is done with the function key, if you were wondering.)
From what I understand, though, TextExpander’s SDK is quite easy to implement, so it’s also a question of other developers acknowledging that it’s a worthwhile and desired addition to their applications.
I’m not sure I’ve seen it mentioned here, but the native iOS/iPadOS/AND macOS feature now entitled “Text Replacement” is certainly worthwhile for anyone looking for something like TextExpander. It can easily be made to function quite similarly.