Siri can't hear internal mic on MacPro

Restart the computer holding down the command - option/alt - P - R keys before the gray screen appears. Continue to hold until you hear the startup chime for the second time. You may need to do this 2-3 times.

Reset NVRAM/PRAM

Try a SMC reset. The article covers when this is required, but doing this will not affect anything.

Reset SMC

It's hard to tell what "all the other solutions" are that you read on a "different thread". Can you list what you've tried?

MacPro internal mic? Not sure there is one... Is there one on my 2010 MacPro 6core Westmere? I got Siri to work on it by plugging a mic into a usb audio interface.

There is no internal mic in Mac Pros. The OP probably has a MacBook Pro. A lot of what gets posted here about “Mac Pros” is not about Mac Pros. Unfortunately.