I did a clean install of Ubuntu 19.10 on a new computer. Since GTK2 was not installed, I needed to install it:
sudo apt-get install libgtk2.0-0
after this, the Lazarus programs launch, but only after a ~20 second delay. Once the GTK program is running, all is fine. But ANY Lazarus GTK2 app takes a long time to start - regardless of whether it is the large IDE or a small application.
Fortunately, Ubuntu 19.04 seems to ship with an intact copy of libqt5 (unlike 18.04 where one needs to rebuild bindings), so one can simply install
sudo apt-get install libqt5pas-dev
The IDE and all my programs nicely compile to QT5. Very impressive.
One final issue, when you recompile the Lazarus IDE, if regenerates the "Lazarus" executable but not the "startlazarus" executable. If I look at the recompiled "Lazarus" it uses QT5, but the "startlazarus" remains gtk2. If I launch Lazarus with "startlazarus" I get the long delay before it calls "Lazarus" while if I run "Lazarus" it launches immediately. Does anyone have any idea why GTK2 applications on Ubuntu 19.04 have this long delay, and if there is any way to eliminate the delay?