Seeming spontaneously, a calc document became corrupted in a way addressed by question:
“I can not open my spreadsheet it comes up with this error: Read-Error. Format error discovered in the file in sub-document content.xml at 2,72157(row,col)”
There is no reason to suspect file corruption.
Instead, the problem appeared after saving a document with a ‘>’ character as the last character in a text cell.
Could this be a bug in Calc?
Which version of LibreOffice and which operating system? What was the full content of the cell and can you repeat the fault by putting only that content in a new spreadsheet?
…and which filetype to save to, which history of the document?
Trying to help here I had a dozen-odd files (not only spreadsheet) showing a similar error. In most if not all of these cases the document had a history including saves to alien formats, sometimes akso editing on different systems, recording changes and so on.
If I had the file I might find remedy.
Please take a look,
It would still be interesting to investigate the suggestion by @mkreich that a particular cell entry can cause the problem. If it can be repeated we might provide feedback to developers via bugzilla.