I am not sure if your problem is that autocomplete is not working or that the commands will not run at all.
If you type the three letters lib does a menu of possible completions appear? That is what I would call autocomplete.
If you type the following command in the code pane
library(tidyverse)
and then, with the cursor still on that line, type CTRL + Enter (that is holding the CTRL key down while pressing Enter) does the command execute?