From the latest Undertale / Deltarune newsletter, which also has an update on Chapter 3 (Deltarune Chapter 2 came out almost exactly two years ago):

We are continuing to work on Chapter 3! The Chapter got playable from beginning to end. After some restructuring and reshuffling of different parts, it’s feeling quite good to go through. Can’t say it’s finished yet, but the unfinished parts are certainly seeming less and less numerous. That’s good because try as I might to sleep, until the game is finished, I’ll see nothing but nightmares...

Earlier, we were considering having a stealth-focused section in the game where you would slowly, slowly sneak around certain areas.

After developing some concepts, we realized a mechanic which basically just makes you move slower isn’t necessarily fun.

So, we didn’t do that...

Anyway, feel free to listen to this song since it’s now unused.

It’s a great song. Imagine if Toby Fox wrote a song for a stealth section in a video game — I’m guessing it’s pretty close to what you imagine.