How to prevent new windows stealing focus in Lubuntu 20.04 (Ubuntu with LXQT)

I've seen some solutions for this problem (preventing new windows of stealing focus) for Ubuntu with Copmiz, but cannot find anything for Lubuntu 20.04 (which uses Lxqt with openbox, and optionally compton). I've tried to disable compton but still, for example, I am showing a presentation and a new window pops up (for example, the upgrade notifier) covering my presentation. I would like the new windows to remain below, and just get the focus when I choose to.

Any idea about how to get this in Lubuntu 20.04?

Thanks in advance.

The rc.xml configuration file of Openbox (typically ~/.config/rc.xml) contains a block. Change the value of focusNew to no.