I have the physical ver. of the essential kit. I used the code to redeem it in DND beyond, and I want to create characters for it, however the content from the kit isn't showing up in the character creation section. Mainly, my bard want to have the entertainment background and couldn't find it...

The entertainer background is in the players handbook not the essential kit, unfortunately. To use the entertainer background  you would need to either buy the players handbook  or buy it individually on dnd beyond.

That's weird. It defiantly is one of the five suggested background in my essential kit. This is my first time playing D&D, and the first time I learned about Backgrounds, so the only way for me to learn about the entertainer is from the essential kit...

I believe that code only unlocks the adventures, not any character options (taken from this thread)

So you should be able to see this page (Dragons of Icespire Peak adventure)

But not this page (Players Handbook)

It should come with a discount code for the player's handbook on the site, which is probably your easiest and quickest way to getting the content.

OK, that's make sense. Thanks!