I think you could try to install the github version of rstan which is not available on CRAN yet.
install.packages("rstan", repos = c("https://mc-stan.org/r-packages/", getOption("repos")))
Or any of the proposed solutions in this thread: Can't install latest version of Rstan
If the worry has to do with memory, than cmdstanr might still be fine because it does not keep all samples in memory (or at least there is an option to not do that) but saves them to a .csv file.