Keep Google Sheet under a fixed number of rows.

acraCleanup.js

function acraCleanup() {
	var rowsToKeep = 1996; // CHANGE TO YOUR DESIRED NUMBER OF ROWS TO KEEP.
	var rows = SpreadsheetApp.getActiveSheet().getLastRow();
	var numToDelete = rows - rowsToKeep -1;

	if ( numToDelete >= 1 ) {
		SpreadsheetApp.getActiveSheet().deleteRows(2, numToDelete);
	    }
}

gistfile1.txt

// new version
function acraCleanup() {
  const ss = SpreadsheetApp.getActive();
  const sheet = ss.getSheetByName('Data');
  const maxNumDataRows = 1986;
  const numHeaderRows = sheet.getFrozenRows() || 1;
  const numRows = sheet.getMaxRows();
  const numRowsToDelete = numRows - numHeaderRows - maxNumDataRows;
  if (numRowsToDelete <= 0) {
    console.log(`🛑 Nothing to do: sheet '${sheet.getName()}' has ${numRows} rows, which is less than or equal to the allowed max of '${numHeaderRows + maxNumDataRows}'.`);
    return;
  }
  const rowStartKeep = numHeaderRows + 1 + numRowsToDelete;
  const rangeToKeep = sheet.getRange('A' + rowStartKeep + ':Z');
  const target = sheet.getRange('A' + (numHeaderRows + 1));
  rangeToKeep.copyTo(target);
  const rowStartDelete = numHeaderRows + 1 + maxNumDataRows;
  sheet.deleteRows(rowStartDelete, numRowsToDelete);
  console.log(`✂️ Pruned ${numRowsToDelete} rows at the end of sheet '${sheet.getName()}'.`);
}