Hi, Karel-
We haven't done anything with building/using AFNI on Ubuntu 19.* yet. In general, there tend to be minor changes in the way the package manager Aptitude operates to install things on different versions, so we have had to make minor adjustments to installation instructions for different Ubuntu version numbers-- you can see this fact in our varied set of installation instructions for Ubuntu. Sometimes, this takes a bit of time and work-- lately, R installation has caused some minor headaches, but I just reinstalled my OS for ubuntu 18.04 and all the instructions worked fine.
Note that the 19.* versions of Ubuntu are not LTS. The currently most modern LTS is 18.04. We usually focus on the LTS versions, because those are the more stable OS versions.
Personally, I wouldn't upgrade to a non-LTS Ubuntu version without some very strong, necessary motivation (and I can't think of an example situation of such a thing-- doesn't mean that doesn't exist, but it wouldn't be a standard thing to do).
--pt
