Take this with a grain of salt, this take is formed through my own experience and the book "So Good They Can't Ignore You" by Cal Newport.

Job satisfaction comes from being good at your job

At the beginning of your career, you are most likely shit at your job, a lot of pain will be felt, and you will actually start to question yourself, "is this really what I want to do".

Job satisfaction will be low, and if you subscribe to the viewpoint of "do what you love and you'll never work a day in your life", then you will find yourself wanting to quit your job, since you don't love what you do.

That feeling of being shit at your job is a signal that you are being challenged, and if you actually put in the work to get better, you will actually get better.

How do you get better?

Identify the craft, and actually put in the work

There is no shortcut to mastery. Regardless of what you do, there are a set of skills that people value, and that's what they pay you to do. To get better, identify that set of skills (ie the craft), and actually put in the work to improve on it.

Doing the easy thing will not make you better. Deliberate practice is painful, but it will help you improve.

After working on your craft, and actually improving, that's when you actually start getting satisfied at your job.

If you do it right, it's never going to get easy

There's always another mountain to climb, another project to take on. If you do it right, you will continue to take on more difficult tasks and work on more difficult things.

That nagging feeling of being out of your depth is never going away. Accept the pain as a part of being human, stop trying to escape that feeling, that will free you to focus on getting better.