I'd like to submit my own game ideas, how can I do that?

Game Idea as Writer in your Page, step by step:

https://itch.io/dashboard
create new project

Title: Game Idea (Godot4 2.5D Platformer collaborate)
Classification: Books - A story told through words

Kind of Project: Html
Visibility: public
fill the fields and submit to save

Later you can take html with images, file management to upload as zip .

Submit game ideas to whom?

I'd like to submit my own game ideas, how can I do that?

That's easy. Create a new thread and post your ideas there.

Though if I'm not mistaken, there is a game ideas thread here but I couldn't find it.