Excel and latest download

Per this "Release notes for Office 2016 for Mac" you should be at 16.16.3

https://docs.microsoft.com/en-us/officeupdates/release-notes-office-2016-mac

Also see

Fixes or workarounds for recent issues in Excel for Mac - Excel for Mac

Read this article, especially the supported versions.

Microsoft Office support for macOS 10.14 Mojave - Office Support

But did you ensure that you have updated Office 2016 to its most recent update after the Mojave update? Even if you did so before the 10.14.1 Mojave update? Something may still be amiss within Excel, and Microsoft may be readying another update to keep up with unplanned changes within Mojave 10.14.1.

Is Excel current?

What is the Office version you are using?

Great!

Now, no excuses not to be creating spread sheets 🙂