@brian-d ,
If I type blah with “append extension” enabled, it calls it blah.txt when saved, which is the exact behavior I would desire.
And in Windows OS, if you type blah. (with the period), that is the way of telling Windows OS “I want the extension portion to be empty: that is, NO EXTENSION, I MEAN IT” … so if the developer were to take your advice, and say “if the user types period, which is the OS’s defined way of specifying no extension, I should ignore the defined behavior and instead use something that is completely nonstandard after 30+ years of DOS/Windows backward compatibilty”, that seems a rather strange option. Especially since all you have to do is not type the period if you want Notepad++ to apply the extension.
If you mean, "I want to enter blah.xyz, and have it save it as blah.xyz.txt, then at that point, just type a couple extra characters. It’s not that onerous: but that’s just my opinion – and since this Community Forum is made up of users, and is not official feature-request tracking, that’s all you will get here in the forum, is opinions and workarounds; the FAQ in the forum explains where to go for actually submitting a feature request to the development team.