Unable to use package in library

I apologize for the embarrassing question as an amateur.
R's sem should have been installed, but the following error appears in the library(sem):

There is no package named ...
Error: Package or namespace loading failed for sem

I tried installing a package equivalent to ... because it says ...And if you do library(sem), now

There is no package named **
Error: Package or namespace loading failed for sem

I have repeatedly seen a display saying **, and after installing **, there is no package with another name.
I would appreciate it if you could tell me the solution.In library(), sem is in the list of installed packages, so I think it's installed, but somehow it doesn't seem to load in library.