Hmm. When I installed the IDE on a fresh VM, and let it start the IDE after the installation finished (the default behavior), it went and installed the AVR board package including drivers and compilers/etc automatically, even though there were no boards at all connected.
I uninstalled (including deletion of the AppData folders) to try to see if this would happen if I didn't let the installed autorun, and instead left it to later, but apparently there are hidden pieces left behind (the drivers?) that prevent the auto-install. So the 2nd time I installed the IDE, it did NOT install the AVR board package.