If installed correctly, it typically displays a message such as: "R2R Root Certificate is installed!" . Why is it used?

The file stands for ReadyToRun Certificate Test . It is a legitimate, native software component developed by Microsoft. It is closely tied to the .NET Core and .NET 5+ developer ecosystems. The Role of ReadyToRun (R2R)

When you run R2RCERTEST.exe , it checks your Windows certificate store to see if the R2RCA.cer was correctly imported into the "Trusted Root Certification Authorities" folder.