On OS 9.2.1, how can you access shared files from windows computers?
Mac OS 9 has no built-in support for Windows file sharing. There were third-party file sharing applications for Mac OS to allow access to Windows networks, and there were also Windows server tools which could allow Mac access to Windows servers. One tool I remember using was DAVE, from Thursby software. It used to be a Windows networking kit for Mac, but has morphed into something else now. If you found an older version it might work, but I doubt it would be compatible with the latest Windows.

I'd recommend looking for an FTP server for your Windows machine and a FTP client for your Mac.