I solved the problem in the end but, searching on the internet, this is a recurrent problem and often people do not find an easy answer.
The most sensible explaination (in my opinion of NOT a software engineer) is this one: since i kept trying to install the car package and other auxiliary packages, somehow some directory got corrupt in the process. There was no way I could make the package work without unistalling completely R and R studio, and rebooting the system after EACH step and reinstalling everything.
So I did, and also I installed the packages with the command: install.packages("car", dependecies = FALSE) so that the program didn't get stuck trying to install 30 packages all at once. I think ultimately since car package needs carData package, that needs rio package, that needs haven that needs data.table and so on the process was to much for the software.
I wish some developer looked into it so that no more time is wasted on such issues. I don't think it is acceptable that such a necessary and widespread tool like Rstudio still suffers from such silly defects.