I have a similar issue/problem as this post except that my entire site won't build. I have the academic theme from like... 2017 and have been having a hell of a time trying to figure out how to update it.
I updated the theme using blogdown::install_theme(theme = "gcushen/hugo-academic", update_config=FALSE, force = TRUE) as suggested, but my config.toml file looks nothing like the one posted.
Just updating the themes folder won't update the config structure, and it also doesn't change the folder structure either. these update notes show that there's a config folder in your root, which isn't there in whatever old ass version of academic that i'm running (v2 i think?)
I love blogdown, but if it's this hard to update your site after only a few years, how can it be sustainable? Or is the hard lesson here to update often?