Has dental technology actually improved lately?

So, what’s actually changed in dentistry lately?

My dentist started working on my tooth—she cleaned out the canals using this specialized needle thing, and then she packed something right inside the root. I went down a bit of a rabbit hole on YouTube and found this

She hasn't quite finished yet because she left the tip unfinished. So now I'm sitting here wondering if it's going to end up looking like the video, where they grind down the outer part of the tooth. Also, at first glance, it looks like something you'd have to pay extra for? Because I'm seeing her through my insurance provider.

I don't remember them doing this before—inserting stuff directly into the roots—so it kind of feels like the tooth might actually be stronger now than it was before.
Actually, I always thought that once you clean the nerves out of the roots, the tooth isn't "alive" anymore... like it starts to decay because it's not getting oxygen or whatever. Is that still true even with this new stuff? Will it still just rot away eventually?

I’d love to hear from any experienced dentists out there. How much has dental tech actually advanced, and where is the whole field heading?
People have been talking about growing teeth using stem cells for ages, but does it feel like that's still stuck in some experimental phase?

Getting rid of tartar and those stubborn buildup deposits doesn't have to be an ordeal anymore; it's entirely possible my new dentist has implemented some sort of cutting-edge technique.

You might think it wouldn't hurt—as if it’s some trivial thing—but honestly, I was sitting there with tears streaming down my face.