Look again at Fedora Silverblue /any other desktop variant. VanillaOSses apx is just a wrapper around distrobox, which is preinstalled on ublue even.
Apx installs apps on containers just as it is possible on Fedora Atomic (the general name for all immutable desktops). You can also layer and remove apps to or from the base OS which is sometimes needed or nice for speed.
On Fedora Atomic you have
flatpak
podman containers (toolbx, distrobox: like apx on VanillaOS but without the great tooling and GUI management, yet)
rootful containers for stuff interacting with systemd, needing USB access etc.
layering or removing packages / changing the OS to something like ublue to let other people do the work, especially for NVIDIA drivers