Hi Dachshund_Decals, I am Paulo and I'd like to help.
Try to save the file with quotation marks and see if it works as a workaround. Let's say you press Ctrl + Shift + S to Save As, enter the file name as "index.html" with the quotation marks. When you include the quotes, Notepad will save the file with the index.html name literally, without adding any additional extensions. The file will still be saved as .HTML even without changing the Save as type to All files.