Do you happen to know which solution solved the problem, for future users to know?
As for what not to run: You do not need to specify a compiler. You may want to include a Makevars.win that has compiler optimizations defined, but not paths to compilers. There are some listed around here, and they look like CXX14FLAGS += -march=native -mtune=native -O3 -Wno-unused-variable -Wno-unused-function -fPIC if I recall correctly. That’s what I have on linux, unsure whether those options hold up on windows. Basically, just avoid modifying paths, or specifying which compiler to use, unless you know for certain what you’re doing. Future versions of R should continue working as far as I know.