ASP.NET: Update and delete without using HttpPut and HttpDelete

I found many open-source projects which do not use HttpPut and HttpDelete for updating and deleting. Instead, they add the HttpPost endpoint before their methods, and the functionalities are implemented successfully as well.

What I learned is that we use HttpPut and HttpDelete to update and delete. I am confused.

I have added examples of update methods and delete methods below.

UPDATE:

        [HttpPost]
        public async Task<IActionResult> Edit(int id, NewInvoiceVM invoice)
        {
            var allInvoices = await _service.GetAllAsync();

            var invoicesValidate = allInvoices.ToList().FirstOrDefault(n => n.SupplierName == invoice.SupplierName && n.InvoiceNumber == invoice.InvoiceNumber);
            await _service.UpdateInvoiceAsync(invoice);
            return RedirectToAction(nameof(Index));
        }

DELETE:

        [HttpPost, ActionName("Delete")]
        public async Task<IActionResult> DeleteConfirmed(int id)
        {
            var invoiceDetails = await _service.GetInvoiceByIdAsync(id);
            if (invoiceDetails == null) return View("NotFound");

            await _service.DeleteAsync(id);
            return RedirectToAction(nameof(Index));
        }

Question: Are HttpPut and HttpDelete required for Update and Delete method? If not, when should we use them?