I think you simply have to press "enter" to get into main menu? Then you move around the menu using arrows. Mouse is not used in this game

Just use a controller
There will be kinda tough plateform parts anyway so you better use a controller

WASD keys and enter.

Been a while since first time I played this and can't remember 100% now if default at first-time startup is WASD and Enter, or arrow keys and Enter. I think it's WASD as default, but if that doesn't work, then try arrows.
Backing out of menus is ESC.
In Settings /Keyboard you can remap keys - I have arrow keys for movement in the game now and pretty sure I chose that myself, and not default.

If you're a casual player on KB then there are a few platforming spots where likely it's easier with controller if you have one. But it's doable without (I'm an example of that myself !). And if you're an experienced KB player in platformers then you'll be just fine too.

A practical tip: Once you've started into the game a bit, then be careful of the fact that 'Exit' in the submenu is Right BUT !!! that in the main menu Right is New Game !! and instead here in the main menu Exit is Up. That has caused some people to lose their unfinished game, when they've been too quick in exiting out of the game and not reading the lead texts ("Are you sure...") properly, but just gone Right - Right. So keep that in mind.

Jump (and double-jump when you get it later in game) is Space as default, and then there's a key for the 'heavy' function for later in the game when you've earned it, and also there's a key for the 'voice' also later in the game when you've earned it - that one comes in right towards the end. 'K' is the default key for the heavy (cube) ability - but you have to earn it first (in chapter Red) And then the voice ability is 'L' on keyboard, and it can be a bit confusing the first time you come across it - as it doesn't actually give sound at first but does a bit later on. This will make more sense when you get there, in the game ;-)

And that's it :-)

You can use WASD to choose the options and use ENTER to get in it. (I just have a keyboard to play this game) The game doesn't need to use the mouse.

Q - sing
W - cube
E - jump/glide
Movement - ⬅︎⬆︎⬇︎➡︎ - arrow keys
I found this to be working using a keyboard
Note: this is custom settings though

引用自 s7ian：

Q - sing
W - cube
E - jump/glide
Movement - ⬅︎⬆︎⬇︎➡︎ - arrow keys
I found this to be working using a keyboard

That isn't default, surely? But must be something you've set or chosen for yourself.

I have as default: K for cube, and L for sing (NB that both abilities have to be earned first), and WASD for movement and ENTER for jump/double-jump (double-jump must also be earned first). As default for keyboard use in the game.