A reader is having an issue with LibreOffice Calc:
“I hope you can help. I am running Windows 10 and was using Calc to create a spreadsheet of my passwords.I have no idea what I hit, but while editing the document, suddenly the text in two cells became highlighted in purple and the entire document was locked. It responds to nothing I have tried. I looked in the online help files for Calc and could not find an answer. Can you help me?”
In LibreOffice Calc should be able to unlock your cell by going to the Tools menu at the top of the spreadsheet.

Here’s the same menu in OpenOffice.

Let me know if it works.