Not in my experience, previously ran it setup externally with a shared library for at least a year or longer, https://support.apple.com/en-ca/108345. Typically I backup to external drive 2 ways, copy of library itself and unmodified export, only had to go through above after I needed to rebuild the laptop. OP app and or https://photosbackup.app/ , seems like they might enhance my setup, will have to take a closer look.

There's some technical reason (or non-reason) why Mac OS does not accept the System photolibrary on an external disk. It prevents certain things from happening which may or may not mater to you. Otherwise you can switch librarys by holding Option during photo bootup.