Thank you for the quick reply!
I have the following RStudio version: Version 1.3.1073, "Giant Goldenrod" (718e6d75, 2020-07-29) for macOS
Where my Rmarkdown package is version 2.5
Here is an example of some code, where the output format yields an error. I have tried to attached the markdown file, although it does not appear to be possible, please let me know if I can do it in another way
library(ISLR)
Smarket <- Smarket
str(Smarket)
this is followed by the following in the preview and .nb.html file
<!-- rnb-source-end -->
<!-- rnb-output-begin 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 -->