I’ve been in your shoes before and when I was more immature I would just browse the Internet and not do much.
However, as I became a more experienced engineer (and currently CTO of my startup), if I ran out of things to do I would think “how can I make this product better?” and just start working on stuff. Or if you can’t figure out what to do on your own, you can always ask your manager or product owners.
From a management and personal growth perspective, you should try to become as autonomous as possible where you provide value even if nobody directly commands you to. This will also grow your skillsets. People don’t like micromanaging other people - ideally you would just be a useful employee without anyone continually asking or assigning you things.
Also just imagine - what if you owned the company? Surely there is something to do that makes it more appealing to the end-users, makes the product better, makes the code quality better, or so forth?
If your issue is you don’t feel incentivized, or are just bored, then maybe look for a new job. If you are just staring into space at work then there are better things you could be doing with your time.