Many music producers opt to send their albums out to a specialized mastering engineer instead of trying to do it themselves (for a review on what "mastering means, see my article Mastering a Song - What Does It Mean?). In fact, I highly recommend that if you are recording an album, and do your own mixing, send your tracks to a professional mastering service for mastering. There are so many reasons for doing this.
One primary reason is that if you are the artist, recording and mixing your own music, it's hard to be objective. And it is VERY easy to start getting into the perpetual search for perfection and never finishing. It's a prime example of perfect is the enemy of good.
Another reason for having someone different do your mastering is that the folks who do mastering for a living know how to do it WAY better than you. they have specialized equipment and highly trained ears. They also have ideal acoustic spaces, which help tremendously in creating a portable (sounds great on anywhere - headphones, car, bluetooth speaker, etc.) finished product.
But be careful not to get lazy about what gets sent for mastering. Having a step-by-step process that you follow after the mix is complete but before the album drops in the mail box can greatly improve the source material that your mastering engineer gets to work with.
You can read the full article here: https://www.musicclout.com/contents/article-181-a-mastering-engineers-guide-to-final-mixdown.aspx