Plus 1 on this - I've probably had direct responsibility for managing fleets of roughly 50,000 linux hosts - never seen an immutable distro. We usually just burn a fresh image of whatever mainline ubuntu is offering every week or two into the fleet. Saying that containers are becoming a defacto standard is reasonable though - pretty much every company I've worked with and my coworkers have worked with have shifted everything into containers (at least in companies with x00k microservice instances running on ~100k machine environments).
WSL2 + Ubuntu. It's either MacOS or Windows in BigCorp with all the Okta/Crowdstrike/... stuff they require - and I like the apt-get convenience.
Most of my time is in Tmux anyways. Over the last 15 years the client side has been one of MacOS, ArchLinux, Ubuntu, and now Windows/WSL2.
The real activity has shifted up to the orchestration and service discovery layers - nomad, k8s, consul, and whatever fleetmanagement/cluster management layers maintains the hosts (a lot of homebuilt + terraform + chef/argo-workflow in our world). It's been years since I was really that concerned about the linux host side of things - why care about "immutable" when the entire machine/image is ephemeral for < 1 week (or in some cases, <1 day) anyways?
