Hello
We are in the final testing for R 4.1.2 and hope to have that available soon. There is a compatibility issue between RStudio 2021.09.0+351 and RStudio Cloud that is not yet verified as fixed, but we plan to upgrade as soon as possible.
Regarding your third question, both phantomjs and java are installed and should be available to your RStudio Cloud projects. There is not a browser installed, so I'm not sure RSelenium will be able to work. Finally, neither svn or zotero are installed, but I have filed a ticket internally so both of those can be considered.
Thanks!
Sam