We had NSSpellCheckerMBS class for macOS for years. But for Windows we had a missing spot in our class lists. Microsoft added spell checking for Windows 8 as a system wide service.
For MBS Xojo Plugins in version 21.2 we add the WinSpellCheckerMBS class to check for supported languages. Pick a country & language specification and initialize a new spell checker. Then you can check some text for error sand get an array of WinSpellingErrorMBS objects. Spell checking may suggest direct replacements, deletions or showing suggestions. We do have a Suggest() function to ask for suggestions and show them the user.
If you like, you can define auto corrections, ignore words and add words to teach the engine your custom words. Optionally you can use user dictionaries.
In general the functions work on Windows 8 and newer except a few newer functions like the Remove method, which needs Windows 10.
Please try and let us know how it works. You may need to develop your own integration to show in text area what is mistyped.