This link is all you need:

How to Install Ubuntu on a MacBook Pro - LaptopNinja
Ubuntu on your MacBook can give your aging Apple product new life. Learn how to install Ubuntu on a MacBook Pro by following this guide.

My Notes

I installed Budgie 20.04 LTS on my old MacBook Pro; it was super easy following instructions from above link to make the install media.

I ran into some issues but they were easy to overcome:

  • You need Ethernet connection from somewhere.  Otherwise you cannot download drivers nor updates.
  • You don't want to use nVidia's driver 340 on (old) MacBook Pro, because Linux will not boot otherwise.  I am not seeing rendering artifacts with 20.04 LTS Nouveau drivers; it is quite usable.  During Linux install, uncheck the option to use proprietary driver so that everything installs and boots.  Then you can enable just Broadcom driver via Additional Drivers later.
  • I had to reboot after installing Broadcom driver for Wireless interfact to work.
  • sudo apt install ubuntu-restricted-extras will give you the missing codecs to support more media formats.