permissions have changed for excel with the new operating system, how do i fix it

If you were using Office 2008, 2011, or even the 32-bit version of Office 2016 for Mac on macOS Mojave or earlier and upgraded to Catalina or later, those Microsoft applications would be unsupported as they are 32-bit on an operating system that requires strictly 64-bit applications. The Microsoft icon would have an (unsupported) transparent circle with a slash through it for its icon indicating you need the current versions of Microsoft applications and a new license. Your documents are fine.

OK, but if you went from a 32 bit OS to Sonoma, a 64 bit OS, all 32 bit apps will not function. Your Excel may be 32 bit.

What was the previous OS?

That may not be your problem, but it needs to be eliminated as a possibility.

Also, if you managed to break activation, Office products will revert to reduced functionality. That may be your problem. That too needs to be eliminated as a possibility.

Excel, Help, Check for Updates

If you moved from a 32 bit OS to a 64 bit OS, no 32 bit apps will run.

What OS did have and what OS did you upgrade to?

What was the fix please?