Transcription spell checker does not respect English(UK) spellings
So the automatic spell checker when set to English (UK) is retaining a lot of US based spellings for a number of words, particularly -ize and izm instead of -ise and -ism, behavior instead of behaviour, etc.
Sacha Goodwin commented
Yes, UK English and this is Mac OSX, Big Sur, Premiere 22.2.0
Just confirming that you did set the spell check language to UK English? And just for your information we are using the OS dictionary supplied by MacOS or Windows. You should find that Premiere Pro will correct words in the same way as the rest of the system.