You can try using addColumn() to add a new column to the table instead of getRange(). Add column expects a number and is zero indexed. So index 0 would map to column A, index 1 would map to column B, etc. Since you want to insert where column B would be that would be index 1. After the addColumn() method, you can set the header name for the new column using the setName() method. You can see an example of how to do that using the code below:
function main(workbook: ExcelScript.Workbook) {
let sh = workbook.getActiveWorksheet()
let tbl = sh.getTable("Table1")
tbl.addColumn(1).setName("Status")
}