"Prioritize" spelling not flagged as error when UK English selected

I would have expected LanguageTool to flag as incorrect the spelling for “prioritize” if the language is set to English (United Kingdom).
In the United Kingdom the spelling should be “prioritise”

I have tried with the “OXFORD_SPELLING_Z_NOT_S” grammar rule enabled and disabled but either way it doesn’t flag the spelling of “prioritize” as an error for UK English.

Is this expected behaviour?

Yes, that word with -ize is valid in English GB:
Screenshot 2022-11-14 at 09-18-24 prioritize - definition of prioritize in English from the Oxford dictionary