Gnome, KDE and also Firefox and Chrome don't seem to be particularly fond of updates being applied under their ass, probably because they are heavy on dynamic code loading and spawning workers with unstable APIs, respectively. Firefox even added some code to detect this and show a blank page with "You gotta restart Firefox before you can open new tabs" instead of crashing.
Edit: Another classic is upgrading the kernel on Arch, not rebooting, then trying to use a thumb drive for the first time since the last boot. Since Arch uses one package for all kernel versions, only one set of loadable modules is installed per kernel package - so upgrading the package removes the loadable modules of the currently running kernel.
I do restart browsers after upgrading them, but that's different from restarting Linux. For desktop environments, I usually don't bother rebooting Linux for anything other than major releases (like GNOME 43/44 and Plasma 5.26/5.27) since most of the minor releases don't make enough of a difference in day to day use to interrupt what I'm doing.
Edit: Another classic is upgrading the kernel on Arch, not rebooting, then trying to use a thumb drive for the first time since the last boot. Since Arch uses one package for all kernel versions, only one set of loadable modules is installed per kernel package - so upgrading the package removes the loadable modules of the currently running kernel.