Ceb
Ceb
I do not really if you have following the office to Configuring C++ Toolchain  If you have do that try to downgrade your R to lower version like 4.0.2...
maybe you can try lower R version like 4.0.2 or 4.0.5， and lower Rtool40， i found R 4.0.2 and Rtool40 can match perfectly
Maybe you should install rstan following this website https://github.com/stan-dev/rstan/wiki/RStan-Getting-Started