Unable to knit to PDF using TinyTeX: Missing *.sty file

I just ran into the same problem with pdflatex. Package grffile was updated several days ago, on 2019-11-08. The changelog reveals the cause:

Recent changes in LaTeX and specifically the release LaTeX2e <2019-10-01> patch level 2 mean that most of the facilities of grffile are not needed, also the changes mean that some of the original patches made by this package no longer work.

This package is now a legacy package that by default just loads the standard graphicx package.

The LaTeX package rollback feature is enabled so that \usepackage{grffile}[=v1] may be used to access version 1(.18) of the package if that is needed.`

I removed all references to grffile from my documents and they compile fine now.