The Steam Client Beta has been updated with the following changes: Steam Input Always show the controller tab in app properties for non-Steam shortcuts Added Invert X and Invert Y to Mouse Regions Scroll Wheel mode can now be chosen from the dropdown in SIAPI games (Inside of Edit Loadout, not Quick Settings) Linux Steam developers can now select which Steam for Linux runtime to use for native titles. Please consult the partner site for more details.
Does anyone know what they mean by “legacy runtime environment”? Do they mean running of the host system libraries rather than Valve’s runtimes?
AFAIK yes
Previously they used library injection and redirection techniques, but the new runtimes are basically containers.