Is it possible to prevent LibreOffice Calc from generating an infinite number of rows while scrolling and instead make it so that I can add a row manually when needed?
The maximum number of the rows is not infinite, but it is a large number. You can not “switch OFF” them, but you can make invisible them. They are not “exist” really (not consupt any storage place) in an specific empty Calc file until you use them.
Hide from Menu:
Select all of the cells (Ctrl-A or by clicking on the empty rectangle near the column A and row 1) - Deselect the used rows - Format - Rows - Hide.
In addition:
Each spreadsheet has 1.048.576 rows x 1.024 columns.
You can check it with Ctrl+Arrow (-down or -right).
If you additionally use the Shift key, the number is indicated in the status line.
See also:
What is the maximum number of cells, rows, columns and sheets in a LibreOffice spreadsheet?
How to quickly get to the last row or column?
How to have the columns numerically instead of alphabetically?