Emi Tanaka, the Executive Editor of the R journal, answering the question "is the R journal still accepting new submissions?", said on Bluesky (8 October 2024):
Actually the last issue was published a few months ago. The issue date lags behind. I believe the current chief editor is/was processing the next one so the next one should come out soon
In addition, you can find this recent presentation (2024) on Youtube by the editor-in-chief Mark van der Loo, where he presents the journal internal working and history, and discusses future plans: https://youtube.com/watch?v=eupuhF7XeVM.
Finally, if you have a look at their github account, their internal tools for publication look like they are in active development (e.g. https://github.com/rjournal/rjtools), with some updates dating from a couple of weeks ago at the time I'm writing this answer.
All of this doesn't hint to the journal being dead :)