It's called Unity. The domain Unity.com was taken, so they had to go with the domain Unity3d.com.
Unity has a free version which you can use for commercial releases (until you make 100,000 or more off your game after which you have to get a license.)
I have no experience with other 2D engines. But, Unity is great in my opinion and has a lot of support. I doubt you will run into limitations.
You can find plenty of 2d tutorials on Youtube for example.
There's a cheap asset in the unity asset store called "PlayMaker" that let's you code visually without writing anything. You basically wire up behaviour in a literal sense.
Or just wait a few months for the follow up to Unity 2019.1 as it's said to include a built in Visual Scripting extension for free.
First of all, Undertale was made in Game Maker... main issue with GM is that the code is interpreted, so it's slow. (Unity and Godot compiles stuff into C++/C#) But you can definitely make complex stuff in Game Maker, especially if you're doing a 2D game (GM's 3D in particular is notoriously slow, and it has no innate 3D model editor or even WYSIWYG level editor)
I can vouch for Godot too, it's specifically made to be easy to use for people that aren't programmers, and after sifting through some basic tutorials I can kinda agree with that. Unity is getting a bad reputation for creating asset flips these days, and they recently did an out-of-nowhere EULA change that screwed over a lot of people. I'd avoid that if I were you, even if it's got a lot of support.
I've done like ONE tutorial and skimmed through the docs, I don't even know how to use it myself yet :P
One of the guys that have written some of the official tutorials is making youtube tutorials, though, might wanna check his channel out: https://www.youtube.com/channel/UCxboW7x0jZqFdvMdCFKTMsQ
