Can't pair Mac Pro with wireless Bose speaker

Are you trying as I suspect to do this via Bluetooth? The Mac supports as standard only the SBC codec. This article https://www.areilly.com/2017/07/29/enabling-aac-and-aptx-over-bluetooth-on-macos/ may help you enable additional codecs.

It could be the Bose does not support the SBC codec.

Check also to see if the Bose supports Airplay, Airplay obviously is supported by the Mac and is generally regarded as far better quality than Bluetooth.

+What exactly happens when you try?

Can you pair other speaker/headphones?

Could it be that the Bose is already paired to another device when you try to pair it with the Bose?