is Office 2011 compatible with High Sierra?

I have both 2011 and 2016. 2011 works fine and 2016 worked fine until they released V16.9 which messed up Excel.

According to MS they are working on the issues but recommend staying with V15.4.1 until a fix is released.

MS Does not support it but depending on your workflow some have found MSO2011 does work in 10.13

Your question implies a concern about upgrading. Read Upgrading macOS without fear and decide for yourself.

You probably already know MS will tell you Office 2011 is no longer supported, but as I understand it, it works for some people. The above procedure will provide a conclusive answer for your particular needs.

Microsoft Office support for macOS 10.13 High Sierra - Office Support