OK, I'm going to assume you mean Pi-Hole and Ubuntu, because your thread title and OP aren't very clear.
I haven't tried, but my guess is that Pi-Hole would be OK on 19.04, but really, there's no reason to try. That release will be out of support at the end of the year and you'll have to jump to another to get updates. Instead, stick with the Ubuntu LTS releases (18.04 being current) or consider Debian 10.1 stable. Both are good for ~5 years, IIRC.
What is Linux 19? Debian latest version is at version 10, Red Hat newest is at 8, Fedora is at version 31, Amazon Linux is at version 2. The Linux Kernel is at 5.2.13. So we are guessing you mean Ubuntu.
So what he is suggesting is either stick with Ubuntu LTS (version 18.04) because it might not work with Ubuntu 19, if that is what you mean by Linux 19. If you are on Ubuntu 19 already, then give it a shot.
I use Debian, Red Hat, and Amazon Linux, so I don't know too much about Ubuntu.