The default keyboard in GrapheneOS does not have a bundled word list for Swedish, but spell checking still worked fine before if I had the "System -> Keyboard -> Screen keyboard (AOSP) -> Screen keyboard (AOSP) -> Text correction -> Customized suggestions" option enabled. After a few days it started showing some suggestions based on my earlier typing, and after a month or two the suggestions were rather complete and high quality. I have used this for over a year.
During December I factory reset my device, and enabled that same setting again, but the keyboard app never learned any word. Beginning February I decided to clear data and cache for the keyboard app, but this also did not help, I have still not got a single suggestion from the keyboard app. The bar with correction suggestions shows up sometimes, but it is always empty when it does.
Now I am uncertain when it all broke. Maybe new words hasn't been added for many months already before December too, without me realizing.
I think this might be a bug, but I am uncertain, maybe there is some other setting I also need to enable or disable?
Can someone confirm what is the steps to enable spelling correction suggestions on the stock keyboard for languages without a built-in word list. Does it work for you?