feat: Gaming on NVIDIA is not offered any more, the SteamOS conversion covers NVIDIA PCs

The conversion installs the patched gamescope on every NVIDIA PC and sets up the kernel parameters, suspend memory and 32-bit libraries on a supported card; it turns off an existing Gaming on NVIDIA.

lib/gamescope-nvidia.sh

@@ -4,8 +4,9 @@
 # https://github.com/theupriser/steamify-gamescope-nvidia; the package `steamify-gamescope-nvidia` is built here, on the PC,
 # and replaces `gamescope` (it provides it). The patch is opt-in: gamescope reads `gamescope_drm_gbm_scanout=1` from its
 # environment, which is set for the gaming session (gamescope-session's environment file, and environment.d).
-# Used by the SteamOS conversion (`gaming_enable`/`gaming_disable`) on a supported NVIDIA card (`nvidia_supported`):
-# GTX 16 / RTX 20 series or newer (Turing and later, what NVIDIA's open kernel driver supports).
+# Used by the SteamOS conversion (`gaming_enable`/`gaming_disable`) on every NVIDIA PC (`nvidia_present`); the kernel
+# parameters and the rest of lib/nvidia.sh's setup only on a supported card (`nvidia_supported`): GTX 16 / RTX 20 series or
+# newer (Turing and later, what NVIDIA's open kernel driver supports). Tested on an RTX 5080 only.
 # Sourced by steamify.sh; not meant to be run on its own.
 
 GSN_PKG=steamify-gamescope-nvidia
@@ -60,9 +61,12 @@ gsn_env_disable() {
 
 gsn_enable() {
     # Only on a supported NVIDIA card; elsewhere the stock gamescope is right.
-    nvidia_supported || return 0
-    # What NVIDIA's DRM stack wants (lib/nvidia.sh): modeset/fbdev on the kernel command line, the modules in the
-    # initramfs, video memory kept over suspend, the 32-bit libraries. Takes effect at the next boot, like the session.
+    nvidia_present || return 0
+    # A PC that had "Gaming on NVIDIA" on: Steam must not also start on the desktop.
+    nvidia_swap_out
+    # What NVIDIA's DRM stack wants (lib/nvidia.sh; a supported card only, the functions check): modeset/fbdev on the
+    # kernel command line, the modules in the initramfs, video memory kept over suspend, the 32-bit libraries. Takes
+    # effect at the next boot, like the session.
     nvidia_kernel_enable || return 1
     nvidia_extras_enable || return 1
     gsn_install_package || return 1
@@ -74,7 +78,7 @@ gsn_disable() {
     # The setting goes, and what nvidia_*_enable added; the packages stay (patched gamescope, 32-bit libraries), like
     # the other packages of the conversion (steam, gamescope-session-cachyos).
     gsn_env_disable
-    nvidia_supported || return 0
+    nvidia_present || return 0
     nvidia_extras_disable
     nvidia_kernel_disable
 }