MacOS: No mountable file system error

Hello. I'm trying to install the latest RStudio version (RStudio-2021.09.0+351) on MacOS 11.6, but I get this error after opening the .dmg file: "No mountable file system".
I tried downloading the installer again from other browsers to no avail. Does anyone have a fix?

This error may be an issue with your system, rather than the DMG file you are downloading. Here is an article that covers a lot of different things you can check: macOS Error Opening .dmg Disk Image - No Mountable File Systems