Ubuntu is constantly updating something ...
Only because you let it (or have told it to) do so.
It took extreme measures to prevent to prevent Win10 accepting updates, whether you wanted them or not. Win11 is worse still.
Preventing any Linux updating is a simple matter (and Linus won't give a fig if you do).
... and if you're not updating your kernel, you just update if you want, and move on without rebooting. Future versions won't even require reboots for kernel upgrades. That is experimental now.