The purpose of this document is to summarize some of the things I had to figure out to successfully install Ubuntu on my iMac '19 27" 5K, a.k.a. iMac 19,1.
From what I could find, iMac's do not have the t2 security chip. However, it does share hardware (and firmware) with contemporary Macbook Pros. For this reason, the t2linux.org website contains lots of helpful information about how to install Ubuntu on an iMac.
However, the guides on the t2linux website did not work for me when I ran it, so I had to mix and match some old pages from the wiki to make things work. Also, most issues are focused on Macbooks, not iMacs.