InstallR[] works in version 12, but not in Version 12.1
In[1]:= $Version
Out[1]= "12.0.0 for Microsoft Windows (64-bit) (April 6, 2019)"
In[2]:= Needs["RLink`"]
In[3]:= InstallR[]
In[4]:= REvaluate["sample(1:100,10)"]
Out[4]= {76, 84, 1, 79, 97, 16, 65, 73, 81, 98}