How do I migrate data from a Mac Pro (2012) to an iMac (2021). Wi-Fi is not working.

Do not migrate over your local Wi-Fi network, it is unreliable and prone to failure.

The fastest and easiest way to Migrate, is to connect the old Mac's Time Machine drive to the new Mac and migrate from it during the initial setup. You my need a USB-C to USB-A adapter to connect the TM drive to the new iMac.

The next best option to Migrate, is to establish a direct Ethernet connection between the two Macs. It will be slower than migrating from your Time Machine backup but it's doable.

see > https://support.apple.com/en-us/HT204350

Here are instructions for the fastest and most reliable method.

Setup Assistant and Migration Assistant

Follow them and your migration should be extremely smooth.