couldn't use microsoft office?

If you are using Office 2019 on Mojave, Microsoft's Autoupdate will now block version updates) because Microsoft now only supports macOS Catalina and later. If you upgraded to Catalina or later from Mojave and Office 2011 for Mac, then that 32-bit application suite is deactivated as incompatible. You will need current Microsoft Office software and licensing, whether subscription via Microsoft 365, or single-purchase Office 2021 for Mac.

If you are on Mojave or earlier and removed Office 2011 for Mac, and then attempted to reinstall it, the license servers are deactivated and you cannot reinstall/license it.

Depends on the version of MS Office. 2012 version is upgradable to work with High Sierra and Mojave. It is 32 BIT so won't go any further unless you run it in a virtual machine such as Parallels in Catalina and Big Sur. You are only allowed 5 installs and then it craps out never to be used again - I found out the hard way while setting up my virtual machine. It is not widely publicised but the version prior to the latest release (Office 2019) is always available as a one-off purchase for peanuts from online software sellers. Going as cheap specials at moment as the 2022 version is just around the corner.