Unfortunately I think you misunderstood and messed things up.
First let me just say that if you are using RStudio, you should not need anything else - just install latest version and that should work.
Now, let's go back to what we discussed.
This was your first issue: R not found. So I sent you to the doc Quarto - Using R that mention setting the env variable to help found a R version if not in PATH
You can override the version of R used by Quarto by setting the
QUARTO_R environment variable.
Then you said you add issue with RStudio render with Quarto Error - #3 by Harlananelson
It bundles Quarto you should not need to install it elsewhere.
I suggest you follow the doc and clean a bit your environment. If you are touching the environment variable, you should understand to which value you need to set it. e.g
QUARTO_R is for the R installation folder for Quarto to use not the QUarto installation. Hence the issue.
Hope it helps