Old I-Mac maxed out with the Big Sur version and I cannot find a Microsoft Office suite compatible

I have an older I-Mac that worked well until I upgraded to macOS Big Sur (11.7.10). Now my Microsoft Office version no longer works. I purchased Microsoft 2021 Student and Home edition and could not install because it requires version (12) or higher. BTW the Microsoft Office description stated it works on Windows or MAC without the details.

Do I have any options without purchasing a new I-Mac?