Generally no. There are some parts of your system that you will have to reboot for (like the kernel). But apps? Installing a new service?
No.
Most systems you just install the app you want, and run it.
There are some immutable distros the require things that are installed as part of the base system to only be available after a reboot, but they provide ways to install things without making it a part of the base system. Thus no reboot required.
Reboot to install software?
Generally no. There are some parts of your system that you will have to reboot for (like the kernel). But apps? Installing a new service?
No.
Most systems you just install the app you want, and run it.
There are some immutable distros the require things that are installed as part of the base system to only be available after a reboot, but they provide ways to install things without making it a part of the base system. Thus no reboot required.