I am also having this problem -- here are the outputs requested from BrainFood.
adamsteel$ R RHOME
/Library/Frameworks/R.framework/Resources
adamsteel$ ls -l /Library/Frameworks/R.framework/Versions/*/Resources/lib/libR.dylib
-rwxrwxr-x 1 root admin 3655012 Mar 5 2020 /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libR.dylib
-rwxrwxr-x 1 root admin 3655012 Mar 5 2020 /Library/Frameworks/R.framework/Versions/Current/Resources/lib/libR.dylib
3dMVM -help
updating R_LD_LIBRARY_PATH ...
oo Warning:
Failed to load R_io.so with this error message:
Error in dyn.load(ll) :
unable to load shared object '/Users/adamsteel/abin/R_io.so':
dlopen(/Users/adamsteel/abin/R_io.so, 6): Library not loaded: /sw/Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libR.dylib
Referenced from: /Users/adamsteel/abin/R_io.so
Reason: image not found
Calls: source ... withVisible -> eval -> eval -> set_R_io -> dyn.load
Execution halted
Thanks!