I really want to write something cool. It doesn't have to be useful at all but I would be delighted if it was.
I have completely no idea what I can write, I'm bored of codewars-like sites and their exercises. Programming challenges lists are in large part boring and useless.
Looking for advices or ideas

if you browse the web a lot, look into tampermonkey. run your own javascript on other people's site to make them easier to use. i've got scripts that block users on forums, show narrators on audible library, show genre for books on goodreads, show books available at my library, etc etc.

one of my side projects i never got around to was to add collections back to youtube. instead of seeing all my subscriptions in one place, i wanna see separate places for music subscriptions vs movie subscriptions vs chess subscriptions etc.

Check on some courses on Udemy and look into the course content to see what projects the course covers.

Some python courses cover projects like web-scrapers which are great to show on your resume.
Some nodejs courses cover projects like creating a REST API and chat-app's which is also very job-relevant.
And some frontend courses cover creating beautiful dynamic websites.

And the courses are super cheap! $12 for a course that teaches you $100k+ skills. Worth it? Yes!

Lastly dont give up! There are LOADS of free/paid resources out there to help you ramp up your skills...you just gotta start the hunt

Try digging deeper into what youre good at.

Eventually you will be beyond the scope of what exists and you will make true progress.

Practice ought not feel boring, it should be tough.