What has happened to make my library() just never work?

you are right, it does work.

I then tried to install a bespoke phylogenetics package, Claddis and it failed as it did previously with the tidyverse and ggplot2.

That is, until I tried to install it on the 'R console' itself, where it installed fine and would then work in RStudio. Don't know what it is, but the installation process is going wrong in RStudio somewhere