ECMAScript VS godot

Godot is an option. It features official support for GDscript (similar to python) and c#, but the engine has the ability to add other language bindings that are community-maintained. I cannot provide any feedback on using any custom bindings as when I was tinkering with Godot I used GDscript, but the engine itself is pretty nice and it is open source. Here is a link to a repo that has the JavaScript bindings: https://github.com/Geequlim/ECMAScript

Yes it's possible, you can use the javascript bindings for Godot available here: JS binding godot

You can write in JavaScript if you really like it.

I'm planning to use this soon: https://github.com/GodotExplorer/ECMAScript

Not without a Nintendo SDK license agreement and signing their NDA.

On the other hand, there’s a nice homebrew port you could certainly use that’s been around for years:

https://github.com/Stary2001/godot

If you want to go the unofficial homebrew route, there's always devkitpro and stary's port: https://github.com/Stary2001/godot

https://github.com/Stary2001/godot (this is the only one afaik) but not sure if it still getting updates

There is a native Horizon OS switch port to the open source toolchain, if you are into that: https://github.com/Stary2001/godot

If you have a hacked switch and want to develop for the sake of developing you can try this out. https://github.com/Stary2001/godot I have gotten a game running on my switch with that fork of godot

It may not be as easy as loading an export template, but since the engine is all open-source C++ you can actually port it yourself when you get a Dev Kit (or even port it to homebrew libraries, like this LibNX port of Godot for Switch).

If you just started using Unity, can I suggest that you use Godot or another open source engine instead? If you make the game in Unity, porting the game to Nintendo consoles could be quite difficult without Nintendo's permission, whereas Godot already has a (WIP) Nintendo Switch port.