N ew ipad pro see’s my iPhone 12, but l-phone won’t connect to iPad

How are you attempting to make this connection? What, specifically, are you hoping to achieve in “connecting” you iPad to your iPhone?

Are you attempting to connect one device to the Cellular hotspot of the other. If so, this connection should be straightforward:

How to set up a Personal Hotspot on your iPhone or iPad - Apple Support

If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

Whilst it is technically possible to do so, be aware that Bluetooth pairing between an iPad and iPhone is generally pointless. If your intention is to use Cellular Hotspot features of your iPhone, this link is optimally achieved using the native WiFi hotspot connection - this being a largely automated process. Hotspot connections over WiFi offer substantially greater throughput, range and reliability.

How to set up a Personal Hotspot on your iPhone or iPad – Apple Support

If you still wish to pair your iPad and iPhone over Bluetooth, you first need to manually enable the hotspot feature on your iPhone:

Settings > Mobile Data > Personal Hotspot > Allow Others to Join - set to ON

Next, Bluetooth for both the iPad and iPhone must be placed in Discovery mode:

Settings > Bluetooth (accessing this page will automatically place the device in Discovery mode)

Whilst both iPad and iPhone are in Discovery mode, you can mutually pair the devices.

Again, I must stress, unless you have an unusual “edge case”, pairing of iPad and iPhone over Bluetooth is largely pointless.