How to clear unprotected cells

I have a user that has a spreadsheet that was created in Excel and has some basic macros. What is the best way in Calc to clear unprotected cells from it?

Just use normal Search&Replace (Сtrl + H)

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And if you wanna make sure every cell you can clean gets cleaned replace + with *, but I predict it’ll be very taxing since up to 1 073 741 824 cells will be processed.