Tootlip is essential config when "grouped windows" is used in the panel, currently if compton is enabled tooltip are very transparent (opacity 0) and in compton-conf there is no option to modify this, it should be done directly in the file ~/.config/compton.conf:
wintypes : { tooltip : { fade = true; shadow = false; opacity = 1; focus = true; }; };
The idea is to include this configuration option in compton-conf.
Here is upstream https://github.com/lxqt/compton-conf
Here is the issue https://github.com/lxqt/compton-conf/issues/145