I solved this issue but documenting here in case anyone experiences difficulty using RDCOMClient to send Outlook emails via R.
Using fresh install of Windows 10 Pro for Workstations running as a VirtualBox VM, R version 4.1.1, Rstudio 2021.09.0 (Build 351), and Microsoft Office365 Outlook client (version 2102 (Build 13801.20960 Click-to-Run)).
The following code causes R to crash every time on the last line:
install.packages("RDCOMClient", repos = "http://www.omegahat.net/R")
library(RDCOMClient)
# Open Outlook
Outlook <- COMCreate("Outlook.Application")
# Create a new message
Email = Outlook$CreateItem(0)
I rolled back the R version to 3.5.1 -- and it now works.
Conclusion: RDCOMClient is not compatible with latest version of R (4.1.1).