Except on Android Chrome when you have a Bluetooth keyboard connected. On Android, isn’t it the on-screen keyboard that does the spell checking via predictive text? So you lose this when a hardware keyboard is attached. Some third party keyboards like SwiftKey do allow on-screen predictive text without showing the on-screen keyboard which helps.
It would be useful if Android Chrome could offer in-place spell checking so this is more of a general Android problem that Discourse.