- macOS should be 10.15.5, not 10.14.6
- XCode should be 11.6 (11E708)
- Rstudio should be 1.3.959
- R should be at 4.02
If macOS, XCode, RStudio and R are not at these versions, they must be all at previous versions that sync up.
The error message is obscure. GEkillDevice been reported on RStudio with iMac in the thread referenced, in connection with the Slackbuild package manager and in R.2.7.0. Beyond this only a handful of other posts reference it.
If R was installed on a user level, rather than in /Library/Frameworks/R.framework the error might occur.
My suggestion is to upgrade all the environment to the versions above, taking care to install R from the notarized package on CRAN for all users.