Running Microsoft Office 2004 on a MacBook Air 2017
Can I get round this issue?

Not easily. This is 16-year-old software, and lots has changed since then, so that a modern OS can't run it.

While it is possible to 'emulate' an older computing environment that could run the software, this is complicated.

Furthermore, Word 2004 can't open most modern .docx files, which were introduced in 2007. So it wouldn't be very useful to you anyway.

Software has a time to live, and a time to die. Either buy a new version of Office, compatible with your OS, or use a free Office 'clone' like LibreOffice. You can read and save Word files from Apple's Pages, too.