Difficulty installing dev version of ggplot2 due to rlang::is_list not being found

Make sure that you're installing your R packages in a clean R session. If you already have rlang loaded when you attempt to install a new version, it's possible that installation can (somewhat quietly) fail when attempting to copy over rlang.so, which would leave you with a temporarily broken rlang.

I would recommend trying to reinstall both rlang and ggplot2 in a clean R session.