I'm always bored, what's some fun stuff to do on my iMac?

Apple Arcade is filled with games and fun stuff, but does require a subscription.

Play games with Apple Arcade - Apple Support

If you are “always bored” go out and do some volunteer work for local charities, habitat for humanity, collecting trash from rivers and creeks, cutting an elderly person’s grass. You’ll get much more satisfaction than sitting around all day playing games. Just a thought.

See also:

Why Neuroscientists Say, ‘Boredom Is Good For Your Brain’s Health.'