This only applies to Windows and I think you're referencing desktops.

Ten years ago I think rule of thumb was uptime of not greater than 6 months. But for different reasons. (Windows Server...)

On Solaris, Linux, BSDs etc. it's only necessary for maintenance. Literally. I think my longest uptime production system was a sparc postgres system under sustained high load with uptime of around 6 years.

With cloud infra, people have forgotten just how stable the Unixken are.