why does my iPhone say device not supported when connecting to my make even after it has successfully paired?

why does my iphone say device not supported when connecting to my mac pro, even though it has already succesfuly paired?

Because Bluetooth connections between iPhone and Mac are not supported, except for Internet Tethering.

Also when I turn Bluetooth on on the phone the devices cog never stops turning (forever serching for a device)

Because while you are in the Bluetooth menu, is when the phone is searching for other devices. Leave the Bluetooth menu and it stops searching.

For what purposes would you want them to talk via Bluetooth? If there was a good reason, they probably would, but Bluetooth is far too slow to sync the gigabytes of data an iOS device can store.

Internet tethering is connecting your computer to the Internet using your mobile phones Internet connection.

iTunes automatically syncs voice memos to your iTunes library when you connect iPhone to your computer.

It couldn't be much easier than that as you don't actually have to do anything more than normal.

This lets you listen to voice memos on your computer and provides a backup if you delete them from iPhone.

Voice memos are synced to the Voice Memos playlist. iTunes creates the playlist if it doesn’t exist. When you sync voice memos to iTunes, they remain in the Voice Memos application until you delete them. If you delete a voice memo on iPhone, it isn’t deleted from the Voice Memos playlist in iTunes. However, if you delete a voice memo from iTunes, it is deleted from iPhone the next time you sync with iTunes.

USB syncing is far faster than Bluetooth.