If I were you . . . I would get a newer version of Excel and install it on your Windows 10 PC now.

You can open Excel 2000 files in newer versions of Excel, then save them in the new format. You may have a few minor issues to iron out, but nothing difficult.

Then you will be ready if you are forced to change your PC to Windows 11.

Finally just an opinion - I don't think that the world will come crashing around your ears if you continue to use an "unsupported" Windows 10 PC. Obviously Microsoft want you to think that it will, but they are hardly an independent arbiter !