how can I launch Steam from Lutris with a follow-on command?
-> “GDK_SCALE=2x steam”
I have Pop_Os! 19.10, unfortunately Steam is usually extremely small at my display.
In which field do I enter this exactly? Custom executbale for the runner?
GDK_SCALE=2x is an environment variable which can be set up in several ways; the default way of doing so for Lutris is by adding a line to the Environment variables table in the System options tab of the config in question (you may want to do it in the global Steam runner config).