There is a program called needrestart which you can run after updates to see what needs restarting to load new copies of libraries etc. Generally speaking you only need to actually reboot for kernel updates.
When you update, you update everything - OS and apps all in one go unless you manually install stuff yourself outside of the package manager. Updates take from seconds to a few minutes unless you are running Gentoo in which case its from minutes to days or even weeks whilst your compiler crunches its way through vast seas of source code and you fix the various issues along the way 8)
You can automate the whole thing or not - up to you.
Grandparent was a facetious question intended to deflate the great-grandparent, which suggested that Windows' annoying need to restart for every damn thing was comparable somehow to Linux's update requirements.
Which as parent points out are functionally nonexistent, except for a rare kernel update (and you don't have to restart if your glasses are thick enough to live patch).
I often suggest Manjaro, which is smart enough to do all the updating for you, but is also Arch enough to let you do it all manually.
When you update, you update everything - OS and apps all in one go unless you manually install stuff yourself outside of the package manager. Updates take from seconds to a few minutes unless you are running Gentoo in which case its from minutes to days or even weeks whilst your compiler crunches its way through vast seas of source code and you fix the various issues along the way 8)
You can automate the whole thing or not - up to you.