The US English dictionary does not work. The default install has no word list. The UK English does. So everything is in a form of English other than USA.
This is a long standing problem going back several revisions. Obviously the developers never use a USA spell checker. Maybe it is just reverse discrimination.
Sad. I’ve used Sun Office, which became Open Office and now Libre for many years. It used to be more limited but real solid technology. Now it seems everyone is more interested in bloatware gadgets than in basic value proposition features. Sad.