You were able to solve the issue by changing the global config for encoding to utf-8? I was under the impression that solved the issue for a previous version.
Without access to your system, I can only guess at what the permissions look like. The file would not be read-only. RStudio would not have read permissions for the file. If it has write permissions for the directory, then it can overwrite the file, even though it can't read the original.
I suggest checking that RStudio has read permission for a file that appears empty, but that is known not to be and still shows up in the open files dialog.
Do you meaning running R directly from a WSL terminal or powershell?