ipad pro cannot “airprint” with a compatible printer (brother HL 3170CDW

If your Printer is set-up correctly - and has joined the same WiFi network that is hosting your iPad - should you continue to experience difficulties, your WiFi Router may be unexpectedly failing to pass Apple Bonjour traffic on you local network, or your WiFi Router and/or Network Switch may be blocking this device discovery protocol.

The Apple Bonjour protocol uses mDNS (Multicast DNS) UDP port 5353.

You may find that restart of your network components will resolve the problem. You’ll need to restart your network devices in the correct order. Assuming that you WiFi Router provides DNS services for your network, restart devices in this order - allowing time for devices to fully boot/restart prior to restarting other devices:

• WiFi Router
• Upstream wired Network Switch(es)
• WiFi Access Points / Network Extenders
• Other fixed infrastructure devices - such as Printers
• Client devices

Restarting your iPad, after restarting other devices in the correct sequence, is most simply achieved by a forced-restart of the iPad:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

First, ensure that you have updated to the current version of iPadOS. The tags appended to your post suggest that you are running iPadOS14; as such, it is recommended that your iPad is running either iPadOS 14.8.1 or 15.2.

If you continue to have difficulties, check to see if your iPad is using the new WiFi Private Address feature. This feature is intended to provide additional privacy and security when using “public” (untrusted) WiFi networks.

Settings > WiFi > [Your WiFi Network / SSID] - tap the “i” icon - Private Address

The Private Address feature is largely unnecessary for your home WiFi network; if enabled, Private Addressing can interfere with anticipated operation of other devices, such as AirPrint. In such circumstances, you may need to disable this feature - and can be enabled or disabled for each individual network.

Use private Wi-Fi addresses in iOS 14, iPadOS 14, and watchOS 7 - Apple Support

Hi Chaeson, thank you for posting in Apple Support Communities.

Apart from the compatibility issues which you have confirmed and the above link that explains very well how to AirPrint, can I suggest the following:

• Confirm if both devices have the latest iPadOS and HP firmware installed. I noticed the post indicated your iPadOS is 14 and we are currently at iPadOS15.2. The following link explains how to update your iPad https://support.apple.com/en-au/guide/ipad/ipad9a74c576/ipados, and
• Confirm that both devices are on the same WiFi network as AirPrint uses WiFi to communicate.