Never mind. I did
] rm FFTW
] add FFTW
restarted Julia and typed this in the REPL
> using FFTW
got (no mention of LinearAlgebra)
ERROR: LoadError: FFTW is not properly installed. Please run Pkg.build(“FFTW”) and restart Julia.
Did as advised and all seems to be well. Is there a reason my first attempt failed?