Programming and reading.
There is no single standard DE on Linux. KDE and Gnome are the biggest ones, and most distros ship with flavors for either. So is KDE non-standard if I install it on regular Ubuntu (which ships with Gnome)? And besides, as the commenter above said, wlroots is one of the few big participants in deciding the wayland protocols, so they are most certainly standard, as standard as any wayland compositor.
Opening a new terminal should work, since those commands you posted affect just the running shell. If not, you broke something else.
Edit: Assuming you pit that export line into ~/.bashrc, just remove it. You might need to enable showing hidden files in your file explorer, them edit it as a text file.
The value of this header cannot be set via JavaScript, so the server can assume that a) if this header is present, then the client is a web browser, and b) the value of the header can be trusted.
This is already obviously wrong. It cannot be set from JavaScript, true, but any other client including scrapers may set it. So (a) is completely untrue, it being present implies nothing and (b) is also untrue by the nature of networking. You can only assume that it either came from a browser without manipulation, in which case the value can be trusted, or from an external source, in which case the attacker may set an arbitrary value.
Steam does not dictate what is standard on Linux. Just because they have not tested with this setup does not mean it isn’t standard.