How does one start Love2d? I read it's pre-installed

I clicked on it in the main menu but all that’s there is some game called 909

Just like Roms and emulators, love2d is the engine used to run games written in the Love language.
This is different to say, Pico-8 that starts its own environment. Think of that as a fantasy game console I guess?
That 909 game is a pre installed game that comes with the game shell. Come to think of it, I haven’t actually tested it on recent OS’s; in particular running it from the Love directory.
There is another shortcut to the 909 game in the Indie Games folder, which is a shortcut to the same file.
On a similar note, Cave Story isn’t a standalone game. It requires the use of a core within Retroarch; similar to how 909 depends on the Love game engine.
Hopefully this makes sense and I didn’t just confuse you more!