Hi, @eieona, and welcome. I have the same set up as yours, and both RStudio and the R IDE return the same error message
> 5 = 10
Error in 5 = 10 : invalid (do_set) left-hand side to assignment
I have Preferences | Code | Diagnostics check for the first two boxes.
It seems unlikely that the underlying R version would affect that, but just for completeness what version are you using? I'm on 3.6.1