This console is incredible! I'm a developer, and I have one question: How can I make something like this myself?

That's a pretty broad question, so it's a little tough to answer, but I'll try and talk about what I did to make Dreambox.

The thing with Dreambox is that I started with a strong idea of what I wanted it to feel like, and what kind of capabilities it should have, and from there started trying to answer more specific questions (like, "how do people make Dreambox games?" -> "they should be able to use native languages like C++ or Rust to make games", "how should playing a Dreambox game work?" -> "games should be bundled into single files that users can drop onto the Window to play", "what 3D capabilities should Dreambox have?" -> "developers should be able to submit vertex-colored and textured geometry, but no shaders or render textures").

From there I guess I just tried to narrow down exactly how each of those worked. Like, I knew I wanted people to be able to use C++ or Rust, so I decided on using WASM because both of those are relatively easy to compile to WASM and there are ready-made runtimes I could use to execute WASM code so I wouldn't have to spend too much time on that aspect.

For Dreambox I also picked an environment I was very familiar with, so it's written on C# and FNA3D as I am very familiar with both. This reduced the amount of effort I was spending learning something new and made the development process go faster.