Has there been a build for a Canon D90?
This is a wrong section for questions.
Consider asking in General Help Q&A (https://www.magiclantern.fm/forum/index.php?board=4.0) or in General Chat (https://www.magiclantern.fm/forum/index.php?board=26.0)
Regarding your question:
No, there is not a build for 90D. but in general there an active development on DIGIC 7/8 models ( 90D is DIGIC 8 ). There is no active developer who has 90D to work on it.
Mostly ML Development is slow, and it's being done in spare time as hoppy, so no builds in near future (probably until years from now).
Well, if have 90D and you are willing to help in development, please let us know so we can give you the forward steps :).