Inserting line breaks in LibreOffice Calc spreadsheet cells
To insert a line break in a spreadsheet cell, press the Command Ctrl+Enter keys.
This will work only with the text edit cursor inside the cell, not at the input line. So first double-click the cell, then single-click at the text position where you want the line break.
You can search for a newline character in the Find & Replace dialog by searching for \n as a regular expression. You can use the text function CHAR(10) to insert a newline character into a text formula.
Formatting LibreOffice Calc cells for automatic line wrapping
Select the cells for which you want an automatic line break.
Choose Format - Cells - Alignment.
Select Wrap text automatically.
Inserting line breaks in LibreOffice Writer text document tables
To insert a line break in a text document table cell, press the Enter key.
An automatic line break will be performed while you type across the end of each cell.