how to connect my iPad Pro and Mac mini with Bluetooth?

What do you want to do when you've paired them?

If you want to use the iPad Pro as second display for your Mac see this Link and follow the isntructions provided

Use an iPad as a second display for a Mac - Apple Support

If you want to use universal control to control your iPad with your mac's keyboard and mouse see

Universal Control: Use a single keyboard and mouse between Mac and iPad - Apple Support