unable to remove file that really exists - fatal: pathspec ... did not match any files

Your file .idea/workspace.xml is not under git version control. You have either not added it yet (check git status/Untracked files) or ignored it (using .gitignore or .git/info/exclude files)

You can verify it using following git command, that lists all ignored files:

git ls-files --others -i --exclude-standard

$>git add .
$>git rm file_Name  

It works. You add new file using right click -> create new file, and immediately delete it after that. The file would go to the untracked file list.

I know this is not the OP's problem, but I ran into the same error with an entirely different basis, so I just wanted to drop it here in case anyone else has the same. This is Windows-specific, and I assume does not affect Linux users.

I had a LibreOffice doc file, call it final report.odt. I later changed its case to Final Report.odt. In Windows, this doesn't even count as a rename. final report.odt, Final Report.odt, FiNaL RePoRt.oDt are all the same. In Linux, these are all distinct.

When I eventually went to git rm "Final Report.odt" and got the "pathspec did not match any files" error. Only when I use the original casing at the time the file was added -- git rm "final report.odt" -- did it work.

Lesson learned: to change the case I should have instead done:

git mv "final report.odt" temp.odt
git mv temp.odt "Final Report.odt"

Again, that wasn't the problem for the OP here; and wouldn't affect a Linux user, as his posts shows he clearly is. I'm just including it for others who may have this problem in Windows git and stumble onto this question.