Yes and no.
As the other commenter said, you can apply live if it has to be (but you absolutely shouldn't).
But, I never have to reboot anyway.
When I install apps, I do that in containers (Toolbox, Distrobox, Flatpak) and they give me all functionality I need.
You basically only install drivers and absolutely essential stuff per OSTree and you only do that once.
Updates get applied and installed in the background for me.
There's no prompt to reboot, they only get staged.
I shut down my PC every few days anyway, and when I boot, I boot into the new image.
I don't see that as a problem. Rebooting is only a matter of seconds on a NVME