After looking at reviews/discussions of several non-Google keyboards that support Japanese, I decided there wasn't a replacement for GBoard that works similarly to GBoard (and iPhone's keyboard) for Japanese. So, I installed GBoard but disabled Networking persmissions. Unfotunately, this seems to have stopped GBoard from working correctly (unless I broke it some other way...).
Japanese has 3 major "syllabaries": hiragana, katakana, and kanji. The way GBoard (and iPhone) usually work is that you type in hiragana, and it offers you choices in all 3 syllabaries, and you click on the one that you actually intend to use in your writing.
What I've found is that using GBoard on GrapheneOS, when you type in hiragana, it offers you only choices in hiragana, but not in katakana or kanji.
I have GrapheneOS's Japanese language turned on. I assume that the issue is that I have networking permissions disabled and that GBoard must be designed to send your hiragana typing to Google, which then sends back its guesses as to the kanji you might be intending to use.
However, it's also possible (I guess, since I don't know) that GBoard usually works in conjunction with a dictionary or something that usually resides on the phone. In that case, I could get GBoard's normal functionality back by installing something.
Can someone clarify either (a) that GBoard requires networking permissions for Asian language support to work correctly or (b) what else needs to be installed for GBoard's Asian language support? Thanks.