I wrote about a related topic here

It suggests ideas about things to do when your "assigned by the manager" task is done, and you (think you) have "spare time" (which is when you may get bored, hence related to this question)

If you are bored at work, you should change it)

Being silo'd causes boredom. This often happens in both large and small companies. Being on the same type of work indefinitely can cause boredom. Needs to be mixed up a bit. This is not a universal thing... some developers like one type of work and don't want to do anything else, but many developers I've worked with like to have variety.

All jobs have some task or other which is tedious. For those things, we put our head down and get it done because it's part of the job.

But I am assuming you're talking about a bigger situation of boredom - being generally bored at work. Common causes...

• not challenged in your current role
  • work out what job you want next and look for opportunities to take on related duties so you can learn how to do it
• not enough autonomy to use "spare" time in a productive way -
  • in tech there is never "nothing to do". The only way you can have literally nothing to do is if you got your assigned work done very fast and you are not allowed to do anything else. Which seems like a weird scenario for a coder.
  • If you have spare time at work and some autonomy - improve something, look into the incoming versions of tools/tech you use, look into areas of the codebase you maybe haven't worked on much. Or, use the time to learn about some other area of the business - do you know how the designers work, or what problems the devops people are solving? Have you ever asked what the finance/marketing/hr people are actually doing? Knowing how your company manages its money, promotes itself and finds new people are good things to understand for everyone.
• have been doing too much of the same kind of task
  • see if you can rotate onto another team
  • or on a smaller team, try learning a key skill from a coworker
  • or just reorder your tasks so you can do something different for a while - sounds simple, but map out the tasks you need to do in the next sprint... are there bad tasks you don't want to do? smash them out at the start. Use the more interesting stuff as motivation.

...and every last one of these has "or, look for a new job" as an option. It's not to be done hastily just because you're bored for a day or even a week or two. But if you are bored for long periods; you've tried everything where you are and nothing has helped; and you have a realistic chance at getting a different job... go for that better job.

Or if you are consistently bored in more than one job - perhaps a career change is in order. This happens! I have a coworker who is leaving a tech job to study sports medicine, because they realised they are passionate about helping people achieve peak physical performance. Want to guess how happy they are? :)

Find a problem that needs solving and either tell your compadres, your boss, and/or begin working on the solution. This is true at any job and for any workplace. This isn't a movie, this is life... And in real life, there's always a problem.

There's always something to do.

1. Work on a (work-related) personal project, e.g. a tool to increase productivity, a POC, create a reference implementation of something, etc...
2. Catch up on TPS reports.

In-life

I believe you are an IT professional. So according to me IT industry is an ocean, and if you go in deep you will never get boredom. But you know, if you swim on the surface, then you definitely get boredom.

At-work

Build stuff which helps the people. And at work, try to support your organization in 360` fashion. And learn at least one new thing before leaves the office.

When boredom starts to hit you at work start looking for new challenges at work. Chat with your manager / supervisor. Start up a new project, innovate etcetera.

If the above does not help start looking for another job.

You are bored when you don't have any real work to do. In most cases, it's a dangerous thing. Here is my take on it:

• Sometimes we like to think that there is nothing much to do at work, which is simply not true. There is a lot to be done and you should go have a chat with your manager/superior about it and find stuff to build.
• A good developer doesn't get bored frequently (can happen sometimes though) and usually finds work to do on their own.
• Developers can have downtimes too. Occasionally, they may not be willing to work (for whatever reason) and tend to believe that there isn't any real task left for them. It happens. The best thing to do is to take a day off, go for a small vacation and come back to work.
• If there is really nothing to do and you are bored, you should consider talking to your manager. Explain them that you are getting bored, and that you would like to build something meaningful. Think of the stuff you always wanted to build, but never got time. This is the right time to experiment with them. Your boss will be happy - trust me.
• After trying out the above, if you are still bored consider spending some time experimenting and learning new things on your own.
• If all else fails, and you are still bored, find a job where you will get a chance to work on something meaningful.

Hope this helps.

Work.

No boredom!